Aircraft Anti Icing De-Icing Operation

Dear All,

Here, we are going to brief some information regarding the DE-ICE / ANTI ICE operation that must be carried out on aircraft which has contaminated ice on its surfaces or suspected to face such contamination.

Please note that the source of this information was the course introduction attended by me at one of Airlines training centers. Neither I added any extra information nor I add any comment.

One of the fundamental principles in aviation is the clean aircraft concept that states aircraft must not take off if critical spots of the aircraft has been contaminated. One form of contamination is winter precipitation such as snow, ice, slush, or frost.

If an aircraft has been contaminated, the aircraft must be de-iced and anti-iced.

De-icing: is the removal of contaminants; the aircraft critical surfaces are completely cleaned.

Anti Icing: is the prevention of contamination, by anti icing you can prevent clean aircraft from freezing again and becoming contaminated with water precipitation.

Some times preventive anti icing is carried out when winter precipitation is forecasted.

BackgroundIn winter weather conditions aircraft surfaces and parts become polluted with ice, snow, frost or slush. Various aircraft accidents have been caused by aircraft surfaces that were contaminated with such pollution. The different forms of winter pollution have an adverse effect on the performance, stability and control of the aircraft. To prevent accidents, aircraft must receive a de-icing/anti-icing treatment in winter weather conditions.

Why is de-icing / anti-icing?

The purpose of the de-icing/anti-icing treatment is to clear aircraft of winter pollution and keep them clear. Winter pollution is any form of ice, snow, frost or slush that has built up on aircraft surfaces or parts. De-icing involves removing contaminants from the aircraft. The critical aircraft surfaces and parts must be completely clean upon departure.The anti-icing treatment protects the aircraft against re-freezing and prevents pollution from occurring. Antifreeze is sprayed onto the aircraft. The protection is temporary. If an aircraft remains on the ground for too long after an anti-icing treatment, the complete de-icing/anti-icing treatment must be carried out again.

Effects of pollution:

If aircraft surfaces and parts are polluted, this disturbs the normal flow of air over the wing profile. This has an adverse effect on the aircraft's lift. The aircraft becomes unbalanced.Winter pollution with frost, snow, ice and slush can cause a variety of problems. A combination of problems can also occur.

Higher resistance and loss of lift:

Pollutants on the wing, especially on the front of the wing, affect the resistance and the lift. The air resistance increases. The lift decreases. The aircraft needs a longer distance to take off and it climbs more slowly. In the most severe case the aircraft cannot take off at all.

Aircraft controls:

The moving surfaces such as the rudder, flaps, slats and spoilers are sensitive to winter pollution. Because there are numerous openings and slits in these moving surfaces, winter pollution easily accumulates. If there is ice between moving parts , the movement of those parts is limited. The aircraft then becomes difficult to steer. This situation also occurs if the same treatment is not applied to both sides of the aircraft. Winter pollution can then accumulate again on one side of the aircraft just before take-off, because that side has insufficient protection. As a result, the aircraft will go out of balance during take-off and may go into an uncontrolled turn.

Engine:

When the engines are running, a strong suction force develops at the engine intake. Ice can be sucked in. As a result, the fan blades and interior parts of the engine can be damaged. Even a small amount of ice can cause serious damage. Ultimately the engine can fail completely. Ice in the engines also affects their power. The power can suddenly drop sharply. The engine power is particularly important during take-off. It determines whether the aircraft gathers sufficient speed to become airborne.

Measuring instruments:

Ice, snow, frost and slush can cause measuring instruments such as pitot tubes, static ports and engine probes to become blocked. As a result, the instruments can give incorrect readings.

What is holdover time?

The holdover time is the estimated time for which the anti-icing fluid will provide protection against winter pollution on the treated parts. Once the holdover time has ended, the anti-icing will stop working and ice, snow, frost and slush will be able to start accumulating again. Sometimes you may just have finished giving an aircraft an anti-icing treatment. The aircraft is clean and ready to depart, but its turn does not arrive immediately and the weather conditions deteriorate. The aircraft appears to be polluted again. You are called up, because the aircraft must undergo a complete de-icing/anti-icing treatment all over again.

Duration of holdover time:

The holdover time commences as soon as the spraying starts. The aircraft must be airborne before the end of the holdover time.

The holdover time depends on:

· the fluid type
· the fluid mix
· the weather conditions

Who is the holdover time important for?

It is important for the aircraft crew to know how much time is left for push-back and taxiing after the anti-icing treatment. The information that they need is:

· Starting time of the de-icing /anti-icing treatment
· Type of fluid and mix (ratio of fluid to water).

What if the holdover time is exceeded?

The holdover time has finished and the aircraft has not yet taken off. Perhaps the de-icing/anti-icing took too long, or the push-back or taxiing took up too much time.

You must make sure that the whole treatment is repeated. A partial treatment is not enough. A new holdover time is then calculated for the new treatment.

I hope that the above information gave you some hints regarding the De-ICE / ANTI ICE operation.

B.Regards

Ayman Shak'ah

Licensed Aircraft Maint. Engineer

A330/A340 Lavatory Waste System

Dear All,


We are going to brief some information regarding the waste system installed on A340/A330. Almost it has the same principle on most Airbus aircraft. A question always has been asked by people. This question is How we can get rid of the waste of passengers in the toilet. Here below we can find some information related to this subject.

Note: The schematic photo is taken from AIRBUS CBT CD / Its here for studying purposes only. It is not allowed to copy it for trading purposes without prior notice from AIRBUS.

The vacuum toilet system is based on the removal of the waste by suction into the waste holding tanks. Inflight the suction pressure is obtained by the differential pressure between the cabin and the waste holding tank. While on ground or at low altitude below 16000 ft altitude the suction is obtained by the vacuum generator because the differential pressure is so low.

The VSC receives signal from differential pressure switch to control the vacuum system generator according to the sufficiency of the differential pressure.

The flush control unit function is to control the flush cycle. When a failure occurs in the flush cycle then the flush control unit will send a signal to the VSC.

The water used to evacuate the waste from the bowl and to rinse the bowl is from the water system. The water valve is of solenoid type valve allows the water to be supplied through the ring into the bowl. Also this valve is equipped with anti siphon. The anti siphon make sure the water direction is to the water ring only.

The flush valve is an electrical motor operated valve. The flushing system is sequenced and monitored by the flush control unit. When the flush button pressed, electrical signal sent to flush control unit at which control the water valve, the flush valve, and the vacuum generator operation. Also the flush control unit interfaces with the VSC.

The left waste tank and its generator collect the waste from the left lavatories while the right waste tank and its related generator collect waste from the right lavatories.

The waste tanks are located in pressurized area of the aircraft aft of the bulk cargo compartment. On the waste tank there is a centrifugal separator that is used to separate water and waste from the air.

The air goes through a demister filter to overboard discharge line. When one waste tank has 80% while another has 70% then the level balancing valve can be opened through a handle on the right side aft of the cabin to use as much capacity of waste tanks during the flight.

Also between the tanks, there is an air shut off valve that also keeps air pressure between the tanks balanced. This valve is controlled by the VSC.

The VSC inhibits toilet operation during balancing or waste tank servicing. Also it interfaces with the PIM and the CMC.
Two of the three tanks are equipped with quantity transmitter the optional tank quantity isn’t displayed. The transmitters send its signal to the PIM via the VSC. Also there are full level sensors one in each tank that signals the PIM via the VSC to give the message LAV INOP.

The waste tanks are serviced from the waste service panel. Mechanically controlled cables will open the balancing valves and the drain valve through a handle. Every tank has its own rinse connection in the waste service panel. When the waste service panel door is opened, the VSC and the flush control unit will be de-energized.

When the waste tank balancing panel door opened, a signal will be sent to VSC that in turn will disable the toilets and opens the air shut off valve to carry out an air pressure balancing in the tanks too.

When balancing is required between the waste tanks, balancing required message appears on the PIM. Also during balancing valve open, VSC will generate message on the PIM LAV INOP BALANCING. Also in the balancing handle panel green light will illuminates.

If after four minutes the waste level balancing valves aren’t fully closed or a fault in the panel switch then the indication green light will start flashing. The VSC keeps the air shut off valve open and VSC will send a message to the CMC - Centralized Maintenance Controller- . LAVATORY CAUTION LIGHT illuminates.

I hope this infomration are helpful to understand the waste system.

B.Regards
Ayman Shak’ah
Licensed Aircraft Maint. Engineer

A320 Landing Gear / Shock Absorber

Dear All,

We are going to brief some information regarding the A320 Landing Gear (Shock Absorber). Below you will find a cross section photo for the shock absorber which will be good to follow while reading the description.

Note: The photo is taken from A320 AMM - Aircraft Maint. Manual- /It's here for studying purposes only. It's not allowed to use it for trading purpose without prior notice from AIRBUS.

1) Compression:

During the compression, the sliding tube goes into the barrel of the main fitting. The capacity of the shock absorber reduces, which compresses the gas. The fluid goes through the damping head and lifts the compression-orifice plate off its seat, to let the fluid flow fully.
Initially, the fluid also flows from the compression chamber to the 1st stage gas chamber, through the first-stage orifices of the damping tube. While the shock absorber compresses, the damping tube and the first-stage orifices go through the damping head. The flow through the first-stage orifices stops, and the flow limits to that through the compression-orifice plate. This produces a two-stage damping effect. The gas compression in the 2nd stage chamber, pushes on the floating piston to help the damping. It also helps to make the damping effect and the compression effect of the oleo smooth.
At the same time, the fluid goes from the 1st stage gas chamber into the recoil chamber, through the openings in the upper bearing. This flow of fluid moves the recoil-orifice plate against the flange of a retaining ring, to let the fluid flow fully. The gas compression and the fluid transfer absorb the shock-loads from the MLG.

(2) Recoil :

The energy in the gas, which is in the 1st stage and the 2nd stage gas chambers, starts the recoil travel. The fluid goes through the recoil-orifice and the compression-orifice plates. The flow of fluid moves these plates to their almost closed position, so that the fluid movement is slow. This decreases the speed of the recoil travel.
A flow of fluid through the first-stage orifices in the damping tube only occurs if the recoil-orifice and the compression-orifice plates go into the compression chamber again. The gas in the 2nd stage chamber helps to make the extension effect of the shock absorber smooth.

(3) Compression and Recoil - 2nd Stage Gas Chamber:

The compression and the expansion of the gas in the 2nd stage gas chamber helps to make the effect of the shock absorber smooth. This is transmitted through the floating piston to the oil and then to the remaining parts of the shock absorber assembly. This procedure helps to make a smooth landing.

I hope the information above is helpful to understand hints of the A320 Shock ABsorber.

B.Regards
Ayman Shak'ah
Licensed Aircraft Maint. Engineer

A340 Fuel System & Distribution / Briefing

Dear All,

Please find below a short briefing about the A340 fuel system, distribution, and sensors.

The fuel system stores fuel in 6 fuel tanks (LH Inner, LH Outer, RH Inner, RH Outer, Center, and Trim).


Note: The photo is taken from AIRBUS VACB CD / Its here for studying purposes only. It is not allowed to copy it for trading purposes without prior notice from AIRBUS.




The fuel is used to feed the engines and APU, controls the position of CG and recirculates fuel for IDG oil cooling.

The fuel system and its related functions are controlled by the FCMS – Fuel Control and Monitoring System-.

The inner tanks are the main feed tanks. They receive fuel from other tanks (Outer, Center, and Trim) by the means of transfer.

The fuel system is controlled by the FCMS which has two identical FCMC – Fuel Control Monitoring Computer -.

The FCMS functions are: 1) Fuel level and temperature sensing. 2) Fuel gauging. 3) Fuel system fault detection and reporting. 4) Control the CG to its optimum position. 5) Fuel monitor and test. 6) Fuel management.

The total useable fuel is 111.08 Tones. The unusable fuel is less than .23% of the fuel tank capacity.

The inner tanks are divided into FWD Inner and AFT Inner. Each tank of them has a collector tank that uses Jet Pumps to keep it always full of fuel. These collector tanks are always full of fuel because the Main fuel pumps and the standby fuel pump are located their. The standby fuel pump operates when the main fuel pump switched OFF or when the main boost pump fails.

The inner aft has main fuel pump and the inner fwd has another main fuel pump.

The inner tank capacity is 33,580 KGS.

The center tank is located in the wings center section. The center tank has two expansion tanks above it to act as the surge tank for the wing tanks.

The center tank capacity is 33,300 KGS.

The outer tanks are useful to provide wing bending relief. The fuel in this tanks transfer to the inner tank when specific amount in the inner tank reached.

The capacity of the outer tank is 2865 KGS.

The trim fuel tank provides extra capacity, CG position is optimum so the drag reduced and the fuel economy is improved.

The trim fuel tank capacity is 4890 KGS.

There is one surge tank at the end of each wing and at the right Hand Side of the trim tank. The surge tank provides tank venting and collect any spilled fuel from the main tanks.

Note: when the refuel operation is completed to the maximum, the fuel can expand 2 % without spillage in the surge tank. The expansion tanks above the center tank allow the center tank to be filled to the maximum.

Access to the wing tanks is done through the man hole access panels and access to the center tank is done through the rear spar. Access to the trim tank is through the THS front spar and through hand holes on the lower skin.

The indicating systems are temperature sensing, fuel quantity, tank level sensing, and MML –Manual Magnetic Level – indicator.

Fuel quantity probes are installed in each tank. Each probe has capacitance value that changes according to the level of the fuel at that tank.

Three compensator probes are installed at the aft of each inner tank and one at the aft of center tank. The compensator probe is of a capacitance type probes. The compensator part has a capacitance which in proportion with the dielectric constant of the fuel changes according to change in temperature.

Two densitometers are installed. One in the lowest part of each inner tank. It measures the density of the fuel and sends the dielectric constant to the FCMC.

Two High level sensors are located in each inner, outer, center, and trim tank. When the High level sensor immersed fully with fuel it will signal the FCMC to close the inlet valve of the related full tank.

Low level sensors (2 in each inner, one in the center and one in the trim) control fuel operation and trigger warnings.

One overflow sensor located in each surge tank. When immersed with fuel the signal sent to the FCMC that in turns closes all the tank inlet valves and the refuel isolation valves.

The fuel temperature is measured through sensor in each collector tank, one in the trim tank and one in the left outer tank.

The recirculated fuel which cooled the IDG oil return to the inner tanks.

2 MML in each outer, 4 MML in each inner and 1 MML in the center tank used to measure the fuel quantity on the ground using the specific gravity and special tables. No electrical power is required.

The FCMC receives data from the FQI probes and the densitometer to give fuel quantity indication.

We have only low and high level sensors in the center tank.

The fuel distribution consists of:

1- Engines, APU feed system.
2- Refuel Defuel system.
3- Main transfer system.
4- Trim transfer system.

The two sections of the inner tank (FWD and AFT) are connected together by normally open EMERGENCY VALVE.

A booster pump from each collector is feeding an engine. Transfer valves are used to isolate each feed system. These transfer valves are opened when cross feeding. LP valves are located one in the pylon of each engine used to isolate the engine feed from the fuel system. This LP valve is controlled through the engine MASTER SWITCH and the FIRE P/B.

There are two APU pumps. One Uses fuel from ENG 2 collector tank and this is called FWD Fuel Pump. Another is called AFT fuel pump that uses fuel in the trim tank through the transfer pipe. The FWD Pumped fuel pass through APU isolation valve and then through the APU LP VALVE while when AFT fuel pumped the fuel passes only through the APU LP VALVE.

The APU FWD fuel pump is used when aircraft on ground or below FL250 (25000FT) with APU isolation valve opened.
The APU AFT fuel pump is used when aircraft above FL250 (25000 FT), or on ground during trim tank refueling defueling, or when fuel low pressure detected from APU FWD FUEL PUMP outlet. It will not operate if the trim tank is empty.

.The refuel/Defuel system controls the fuel flow during refueling defueling. At each wing there is refuel coupling (two adapters) with isolation valve.

Each tank has an inlet valve that allows the fuel to enter the tank from the refuel coupling.

The main transfer system controls the fuel transfer from the outer and center tanks to the inner tanks automatically controlled by the FCMC. Also they can be transferred manually controlled through the overhead panel.

From outer to inner there is a transfer valve when opens the fuel flow by gravity. From center to inner there is transfer pump.

The trim transfer system is to transfer fuel from the center tank to trim tank (AFT TRANSFER) or from the trim to the center tank (FWD TRANSFER).

For the FWD transfer there are trim tank transfer pump, trim tank isolation valve, and auxiliary FWD transfer valve.

When an AFT transfer is required if center tank isn’t empty. The center tank transfer pumps sent fuel via the trim pipe isolation valve and the trim tank inlet valve. If the center tank is empty then the fuel will be transferred from collector cell 2 (LH AFT INNER) and collector cell 3 (RH AFT INNER) via cross feed valves 2, 3 and the aft transfer valves.

The trim transfer is used for optimizing the aircraft performance by putting the CG in the optimum position. The Crew can control the FWD TRANSFER only. The FMGEC provides the FCMC with the CG position and provides excess AFT CG protection.

B.Regards
Ayman Shak'ah
Licensed Aircraft Maint. Engineer

CFM56-5C Thrust Reverser Operation / HCU

Dear All,

Here, we are going to brief the sequence of thrust reverser deployment on engine CFM 56-5C installed on the A340-200/300.

Note: The schematic photo is taken from AIRBUS CBT CD / Its here for studying purposes only. It is not allowed to copy it for trading purposes without prior notice from AIRBUS.


The ECU controls the deployment of the thrust level as follow:

1) Taking direct signal from the TLA -Thrust Lever Angle- while aircraft on ground and engines are running. Or taking a signal from EIVMU through the inhibitation logic when the reverser requisition confirmed by the TCU – Throttle control unit-.

The HCU has a Deploy Solenoid Valve and Isolation Solenoid Valve. Also it has Pressure switch and inhibit switch controlled by ECU for reverser control and monitoring.

2) The hydraulic is supplied to the HCU through the Hydraulic Shut Off valve which opens according to the TLA signal computed in the FCPC – Flight Control Primary Controller-.

3) The ECU will energize or de-energize deployment or stowing solenoids to open or close valves for hydraulic to pass through the HCU – Hydraulic Control Unit- which is responsible for the sequence unlocking, deploying, stowing and then locking the reverser doors.

4) When reverser deployment required both solenoids energized, the hydraulic is supplied to the locking mechanism to unlatch the doors then hydraulic supplied to the stow side, the door and actuator will be unlocked the stow switches will send this indication of unlatched reverser on ECAM (REV In AMBER) then the hydraulic will be supplied to the extend side of the pivoting door actuator. When the door is fully open the deploy switches will close and the deploy signal is sent to ECU and indication appears on ECAM (REV In GREEN). The ECU will de-energize the isolation solenoid.

5) When the TLA set back to normal (STOW) the ECU will de-energizes the deploy solenoid and energizes the Isolation solenoid. The hydraulic is then supplied to the retract side of the actuator piston. The deploy switch will open and unstowed will be sent again through ECU. The hydraulic shut off valve will close.

The HCU -Hydraulic Control Unit- consists of:



1) Isolation Control Valve and its solenoid responsible to supply hydraulic to the HCU. Its spring loaded closed, its two positions valve.

2) Pressure switch signals the HCU of hydraulic pressure availability.

3) Directional control valve and its solenoid supplies the actuator.

4) Flow control valve controls the stowing speed of the doors.

5) Deploy solenoid valve supplies hydraulic to the latches.

The hydraulic supplied, the isolation solenoid is energized the hydraulic will enter the HCU, and then the hydraulic pass through the energized deploy valve to release the latches of the four doors actuators one by one. Then the return hydraulic will return to the HCU to pass through the directional control valve which allows fluid flow to the actuators. Both sides of the piston in the actuator have now hydraulic but due to the differential of the area on the piston sides, the actuator will move in the deploy position. When at least one door start to deploy actuator more than .7% of its travel the stow switch will signal the ECU. This will give REV indication in amber On the E/WD. At 94 % of the travel, the door deployment start to decrease in motion and the deploy switch will be activated. REV in green will be indicated when all doors are deployed. Then the ECU will de-energize all the solenoids and the blocker doors remain open by the aerodynamic forces of the FAN AIR FLOW.

When set to stow, the ECU will energizes the isolation valve while the deploy solenoid isn’t energized. The hydraulic flow in the stow direction on the actuator and the flow control valve will control the stow speed. At 94% of the travel the REV on indication returns amber until it disappears at .7% of the travel.


There are four modes for the thrust reverser. They are: 1) Pre-deployment. 2) Deployment. 3) Stowing 4) Locking.

For maintenance purposes, the Thrust Reverser can be tested on ground through the CMC and be deployed without engines run. The CMC will simulate engine N2 conditions to allow the deployment during test.

The thrust reverser operation logic (AND GATE LOGIC) are: TLA position, Aircraft on Ground, and N2 (Engines are running).

B.Regards
Ayman Shak'ah
Licensed Aircraft Maint. Engineer

RB211 TRENT 700 / Fuel Circuit

Dear All,

Please find below how the fuel flow in RB211 Trent 700 fuel circuit following the schematic attached to this study.

Note: The schematic photo is taken from AIRBUS CBT CD / Its here for studying purposes only. It is not allowed to copy it for trading purposes without prior notice from AIRBUS.

The fuel system is used to receive fuel from the tanks and deliver conditioned metered fuel to combustion chamber. Also some fuel is sent to as a muscle pressure for the AOHE - Air / Oil Heat Exchanger - modulating valve and the VSV - Variable Stator Vanes - actuator system.

THE FUEL CIRCUIT:

The fuel enters the engine through the LP fuel valve in the pylon. It enters the LP stage of the fuel pump and then delivered to the FOHE - Fuel / Oil Heat Exchanger - to cool the engine oil and warm up the fuel. Then the fuel passes through LP filter and then it is delivered to the HP pump.

For the fuel LP filter, there is a bypass that will open in case the fuel filter is clogged.

Some of the HP fuel is delivered to the AOHE – Air Oil Heat Exchanger Valve – and the VSV – Variable Stator Vanes. Another part delivered to the FMU - Fuel Metering Unit-.

Inside the FMU, there is a PRESSURE DROP AND SPILL VALVE that will open in case of high unwanted fuel flow through the FMV. Then the fuel flow and pressure is controlled through the MV – Metering Valve – and the PRSOV - Pressure Raising and Shut Off Valve-.

The EEC - Electronic Engine Controller - controls the FMV to open or close by TM - torque motor -. This MV - Metering Valve - position fed back the EEC regarding its position through resolvers.

After the fuel metered through the FMV, it passes through the PRSOV and then supplied to 24 fuel nozzles after being filtered in the HP filter.

When the PRSOV is closed after engine shut down, there is a mechanically connected DUMP VALVE that will open allowing fuel remained in the manifold to be drained into drain collector tank. This unburned fuel will be sucked at next engine start by the LP pump.

The PRSOV is controlled independently from the EEC by the Master Switch. This will operate the torque motor to close the PRSOV whatever the EEC demand signal is.

In the FMU, there is an OPU – Over speed unit – that will close the PRSOV independently from the EEC if the EEC failure occurs.

Differential pressure switch installed through the LP filter signals the EEC in case of differential pressure is more than 5 PSI.

Fuel flow transmitter signals the EEC regarding the fuel quantity passed through it.

The FF - Fuel Flow - parameter is indicated on the ECAM SD - System Display - ENG PAGE AND CRUISE PAGE. Downstream the LP fuel filter there is fuel LP switch that give signal when fuel pressure less than 70 PSI. It indicates either low fuel pressure or the engine will shut down. As a result the failure will be transmitted to the CMC - centralized Maintenance Computer -.

Two fuel temp thermo couple are as the engine oil sensor signals the EEC as priority control for the heat management system (AOHE) control.

Two Microswitches are used to indicate PRSOV is closed during engine shut down or during turbine over speed test.

This was a short briefing about the fuel circuit in the Trent 700.

B.Regards
Ayman Shak'ah
Licensed Aircraft Maint. Engineer

Human Factors / Research

Dear All,

For 10 years and until date, it becomes very important for Companies Managements, Employees, Decision Makers, and we can say even everyone to study the HUMAN FACTORS.
Human Factors are divided into TWO TOPICS. They are: 1) Physiology Factors. 2) Psychology Factors.

These two topics are important to understand because if someone think that they don't affect his life then he must be sure that they are going to affect others life.

How? When? Why?

I am going to explain this by giving examples on How? When? and Why?

A) Let us start with HOW? WHEN? WHY? from the physiological angle.

We must know about the human body and his senses like hearing, sight sense, smelling, touching, Tasting. These senses are very important to understand that they have functions which will affect taking decisions. Examples on these affected senses in aviation are:

1) When your eyes are affected, then the pilots, maintenance personal,..etc will take improper decisions because they are not able to see things correctly like when an engineer do his walk around for visual inspection or like pilot whe he observes the aircraft parameters during flight or while he reads the check lists,..etc.

2) When ears are affected, then the people working in aviation may make mistakes such as can't evaluate strange noise occurs during flight, or improper evaluation for a noise coming out from the engines while running, ..etc.

3) When the touch sense is affected, then and according to my experience sometimes you can evaluate internal leak for a component by feeling how hot it is after running. So, if I dont have the full ability to feel how hot a component is then I will take a decision to release back a component with internal leak existing and this will make troubleshooting harder.

4) When your smell sense is affected then I can for example see a leak below the wings and I will take a sample from it using my finger and smell it. If the smell sense is affected maybe I will think it is a water condensation and not a fuel leak.

5) If my tasting sense is affected, then maybe hydraulic will come on my lips and I lick it thinking that it is a water and not able to distinguish that it is hydraulic or poisonous material.

In Human Factor You study the human body parts and systems, how it works and what is it consists of. So, when you study it you will know how to care about it and keep it strong senses.

B) Let us start with HOW? WHEN? WHY? from the psychological angle.

All of us are humans, and we know how psycological factors affect us such as stress, environmental atmosphere, pressure, living costs, ...etc these factors will affect the way we take decisions like when you have financial problems and you are on duty flying an aircraft or repairing a component then most of your thinkings will be in your personal problem and this will reduce concentration of the brain on the procedure, safety, and how to troubleshoot.

There are something in the human factors study called DIRTY DOZEN. They are:

1) Lack of communication: like when somebody write a note for his colleague regarding an issue in doing a task. This note can be understood wrongle. So always it must be written in full details or at least without using alot of abbreviations.

2) Complacency: When you do something many times and you didn't find anything changed. then oneday you will say I have always done this check and I have never found anything wrong then I will not do it this time. VERY VERY COMMON AND DANGEROUS THINKING.

3) Lack of Knowledge: When you do something and you reach an area while doing it and you dont know how to do it. You may feel shame or afraid to say I DON'T KNOW. Then the shame will be bigger if you did it and caused a disaster.

4) Distraction: Very common factor. While you are working your mobile phone rings. You answer it and then after finishing the call you complete the job forgetting some points you must do. ALWAYS GO BACK 3 STEPS BEFOREE THE CALL.

5) Lack of Team Work: When you hate to work with someone or when you forget that all of people in the company are team then you will fail. Imagine that there are two pilots one is the captain another is the first officer. If they are not working in the cockpit as a team, be sure that in case of emergency the aircraft will crash.

6) Fatigue: Like working for many hours, not sleeping properly, all what you are thinking about is to make extra money with overtime. You think you are able and you are aware but believe me if you are honest with yourself then think how many times you have done mistakes because you didn't sleep well for days ago.

7) Lack of resources: Like having a problem on an aircraft and you need a part which is not available in your store. You may decide to disregard the problem and say "I will dispatch it". No, Ground the aircraft for sure is better.

8) Pressure: Liek when you get a call from your boss to inform you that you have to finish your job within an hour or less and you know that it takes more. Feeling afraid to lose the job. Believe me LOSE YOUR JOB IS MUCH BETTER THAN LOSING THE PEOPLE LIVES.

9) Assertiveness: A factor like when somebody brought you something to fix and he fill on you orders what to do according to his financial situation or needs of time. He orders you things just because he wants it like this and you know that it is wrong. DON'T DAMAGE YOUR STANDARDS for others to be happy.

10) Stress: Like political news. A war may happen. I will lose my job because of this war and such factors and thinkings. LIVE YOUR DAY, ALWAYS THINK THAT TOMORROW IS BETTER.

11) Lack of Awareness: When you do something always think of the consequences. Build a scenarios for what may happen if I install this here or there.

12) Norm: Like using things as equipment to reduce the time and taking short cuts that you think you are smarter than the manual or the manufacturer instructions. Sorry, you will be stupid and silly because even you succeed one or two times at the end you will fail. DONT DEPEND ON LUCK, THERE IS NO PLACE FOR LUCK IN OUR BUISINESS.

I hope you like such study and research I have done, and I hope we all are going to follow such instructions and make sure to stop doing any of the DIRTY DOZEN.

B.Regards
Ayman Shak'ah
Licensed Aircraft Maint. Engineer

Aircraft Engines Tones / Noises

Dear All,

Can someone distinguish between the aircrfat engine types from its noise?

Let me give you some noise related factors in a way of giving some differences between two types of engines installed on A320/A321.

These engines are V2500 and CFM56-5A/5B.

The V2500 has different noise tone than the CFM56-5A/B. Some of differences related factors are:

1- The V2500 has different number of stages (Compressor Stages / Turbine Stages) from CFM56-5A/B.

2- There are something called noise acoustic panels installed at the inlet of engines. These panels are used to absorb the noise coming out from the engine. Also, these panels are different in shapes, sizes, and material between the V2500 and the CFM-5A/B.

3- Every Turbo Fan Engine inlet air is divided into two parts:
A) Primary Air which goes into the engine compressor stages and turbine stages through the combustion chamber. This air that cause the engine to run. This air will be exhausted outboard. B) Secondary Air that is withdrawn by the fan at the engine inlet and discharged overboard through bypassing around the main engine components and not inside the engine. At the end also the secondary air will be discharged outboard the engine to the air.

Now on the CFM56-5A/5B the exhausted primary air will be discharged seperately to the outboard from the secondary discharged air. The primary air will be discharged through component called "Center Body". On the V2500, it is different as both the primary engine air and the secondary engine air will meet together when discharged in a component called CNA - Common Nozzle Assembly.

This design gives alot of advantages for the V2500 engines. One of the important advantages is REDUCING THE NOISE. Again mixing the discharged PRIMARY AIR with SECONDAR AIR will reduce the noise or at least smoothen it.

4- Every engine type build from different materials, specifications, inlet area, outlet area, valves such as VSV - Variable Stator Valve - , VBV - Variable Bleed Valve, VBSV - Variable Boost Start Valve, number of fan blades, area size of the fan blades,....etc other than the other type of engines.

Believe me, every engine and if I can use the word TONE has different tone from another engine type BUT all engines from the same type has the SAME TONE.

I believe that what I have briefed above are so far helpful information as I also believe we can talk alot about many other factors. But I can say the above are the main factors.

B.Regards
Ayman Shak'ah
Licensed Aircraft Maint. Engineer

ETOPS REQUIRMENTS

Dear All,

ETOPS is "Extended Twin Engine operation". The ETOPS regulation is designed for any aircraft with twin engines.

Why and What are the ETOPS Categories??

ETOPS: This definition is agreed by the ICAO - Internation Civil Aviation Organization -.

This regulation has requirments to comply with it. They are determined by the FAA, CAA, and other NAA.

The Idea of ETOPS is to make sure that any aircraft categorized at specific ETOPS category will fly to its destination over remote land or over water at which no airport will be available through the route.

There are different ETOPS categorizations. Some of them are:

ETOPS 60 MINUTES
ETOPS 90 MINUTES
ETOPS 120 MINUTES
ETOPS 180 MINUTES

That means the aircraft as example like the one certified for ETOPS 60 minutes can fly to a distination through a route at which there will be no airport within 60 Minutes over water such as sea, ocean or over remote land.

Now maybe an aircraft has been certified as ETOPS 180 Minutes. It can be degraded by the ground engineer to ETOPS 120 minutes or even completely degraded to NON ETOPS if the engineer found it not complying to the ETOPS 180 requirments but it is still complying to ETOPS 120 Minutes.

Example for the above situation: An approved aircraft for ETOPS 120 Minutes must have All the three electrical generators operative for the next flight (Two IDGs) and one APU Electrical Generator. The aircraft received by the ground engineer with one IDG INOPERATIVE. Then the engineer will dispatch the aircraft according to the requirments as ETOPS 60 minutes or maybe will degrade the aircraft to non ETOPS.

For the many complicated factors and requirments set by the civil aviations for SAFETY REASONS and REDUNDANCY REASONS many manufacturer noted that it will be helpful to set four engines instead of two and at the same time many airline found it really advantage to use these aircraft especially for flights which need to cross the ocean.

Sometimes, it is really bad to degrade the aircraft from ETOPS to Non ETOPS as this will affect on the whole airline fleet, time, and money.

To eliminate from all of these factors, FOUR ENGINES OPERATED AIRCRAFT is better in my opinion.

B.Regards
Ayman Shak'ah
Licensed Aircraft Maint. Engineer

Inlet Engine Fairings / Shapes / Swirl Mark

Dear All,

Alot of people in the field are always asking why the engine inlet fairings differ from engine to another?? Some of them are cones another are half ball??

What does the Swirl White Solid Line Means??

I would like to clarify this issue in a very simple way giving an example of some engine types.

On CFM56-5A/5B/5C, the engine inlet fairing looks like a cone. This cone has a specific sliding angle which is called (Anti Ice Algebric Angle). According to the studies done by the designers, they have noticed that at this specific angle of cone slide the ice will not accumulate or build up on the engine inlet cone which in some cases it may become dangerous on engine operation.

On V2500, although it is a cone, but the cone slide doesn't have Anti Ice Algebric Angle as it is more acute angle. Instead of that angle, the cone head is made of small piece made from rubber. This peice will keep vibrating while engine is running preventing engine inlet ice accumulation or build up mechanically. (REALLY SMART DESIGNERS).

On CF6-8, the engine inlet fairing isn't completely a cone. It is half ball shape and as we know on this shape, it is almost impossible to be the perfect shape for ice accumulation or build up. Now most of the Engine Inlet Fairings have swirl solid white line. This line will become like EAGLE EYE shape when the engine starts to run. This shape can be distiguished clearly by the birds. The EAGLE EYE shape will make birds frightened from coming near the engine while running and this will prevent bird ingestion or what we call (ENGINE BIRD STRIKE).

Please note that in the near future, you will find alot of photos and schematics explaining most of common questions generated by different people in the field and from passengers.

B.Regards
Ayman Shak'ah
Licensed Aircraft Maint. Engineer

Absolute Pressure / Gauge Pressure

Dear All,

What is the word PRESSURE means? What is the diffrence betwen the Absolute Pressure and the Gauge Pressure?

Pressure is (force per unit area - Pa or psi or mb). It Starts at 1013mb (14.7psi) at sea level and falls at a non-linear rate with altitude. Losing most of its value at the lower altitudes so that at 18,000ft, for example, the pressure is halved to 506mb).

These pressure readings are absolute pressure readings. This means that if an ordinary pressure gauge is open to atmosphere it will read zero. To illustrate the point - checking a tyre pressure with it (say 30psi) the reading will be 30psi. This is called gauge pressure of the tyre. Its absolute pressure would be gauge pressure plus atmospheric pressure = 30 + 14.7 = 44.7psi absolute.

So, in general we can say that

ABSOLUTE PRESURE = GAUGE PRESSURE + 14.7 PSI

B.Regards
Ayman Shakah
Licensed Aircraft Maint. Engineer

Semi COnductors / Dopping

Dear All,

SEMI CONDUCTORS: they are materials which at normal state they are insulators but under certain forces like VOLTAGE, they become conductors. When this force removed, these materials return to its normal state as insulators without causing any damage to the material itself.

They - Semi Conductors - can switch to both states hundred of thousands in a second. They are used in computer hardware. The most famous materials are

1-GERMANIUM
2-SILICON

When no voltage applied, there will be few hundred to few thousands of ohms but when voltage applied, the resistance will drop to zero.

The semi-conductors will become conductors when adding impurity atoms during the growing of crystal lattice. This is called DOPPING.

B.Regards
Ayman Shak'ah
Licensed Aircraft Maint. Engineer

A320 Electrical System / Sources

Dear All,

The A320 has alot of electrical sources. They are as follow:

1- Two AC main buses. Each AC bus is energized from an IDG - Integrated Driven Generator - installed on each engine. The output values are: 115VAC / 90 KVA / Frequency 400 Hz.

2- One main AC bus is feeding something called essential bus and essential shed bus. The shed bus is connected to the equipment at which is important for the safety of the aircraft when buses are lost. When the main AC bus failed, then the another AC bus can be connected to the essential bus to feed it instead of the faulty one either automatic transfer or manual by push button when the auto logic fails.

3- The AC essential bus also can be fed by the emergency generator. This generator is hydraulically powered to give output electrical AC power to feed the AC essential bus. The generator is hydraulically powered by hydraulic pressurized either from the related hydraulic system if the blue hydraulic system pump is operative or by the RAT - Ram Air Turbine -. Note that the RAT can only turn at specific minimum speed on some A320 its 150 KNOTS on another A320 it is 100 knots or until the flaps slats extended.

4- When the RAT stop working, the AC essential bus will be fed from the batteries through a static inverter that will convert the 28 VDC into 115 VAC. So as you can see, the major equipment are connected with essential buses (AC and DC through essential transformer). This essential buses are always fed either from IDG, APU generator, CSM/G - Emergency Generator - using the RAT, and or static inverter. This will give the electrical system a very very high redundancy.

Thanks for AIRBUS.

B.Regards
Ayman Shak'ah
Licensed Aircraft Maint. Engineer

Turbine Inlet Temperature - TIT SENSOR

Turbine Inlet Temperature Sensor (Engine):

The turbine engine is basically composed of different stages of compressors, combustion chamber, turbine stages. Now, when the engine is running, the air will ingested into the engine and will be compressed through the compressor stages. After that the air will enter the combustion chamber as an element for combustion to take place with the fuel. then, the discharged hot exhausted air will leave the combustion chamber under very high in both (Pressure and Temperature). This exhausted air is used to hit the turbine (High Pressure Turbine) causing them to rotate at which in turn will rotate the compressor and so on.

It is used to measure the temperature of the discharged air coming from the combustion chamber and hitting the turbine. the sensing of this temperature is very useful to control the engine operation by the computer that is used this information and according analysis the engine combustion effeciency and at the same time control the power output of the engine automatically through a computer called ECU - Engine Control Unit -. the ECU is a computer that receives different signals from different sensors and systems of the aircraft. One of these inputs is the Turbine Inlet Temperature.

Turbine Inlet Temperature Sensor (Aircondition System):

There is also a sensor called TIT sensor installed on the airconditioning pack. The aircondition system pack. This pack composed of
1- ACM - Air Cycle Machine - (FAN, Compressor, and Turbine)
2- Heat exchangers
3- Condenser
4- Reheater.

Now, the aircondition system is controlled by computer called Pack Controller and another computer called Zone Controller. Now the engine bleed air is delivered to the airconditioning packs to be conditioned both (Temperature and pressure) in the following sequence:

1- the bled air enters the pack via a pack flow valve.
2- the hot bled air enters the primary heat exchanger to be cooled little bit before entering the ACM compressor at which the air is going to be compressed so its pressure will increase.
3- the air will leave the compressor with high pressure and very high temperature due to the compression.
4- then the air will enter the main heat exchanger to be cooled. Then the air will enter the reheater to increase its temperature so we can eliminate any water particle suspended in the air before entering the turbine - The elimination of any water particle is useful to protect the turbine blades from being daamaged or corroded-. Then the turbine will cause the compressed air to extract due to giving force for the turbine to rotate. At this point the air entering the turbine will be so hot and the air leaving is so cold.

Now the computer controlling the system operation needs input to control the flow rate of air entering the packs and also to control the air entering the heat exchangers. Also the computer needs these inputs for maintenance personal analysis and to monitor the efficiency of packs.

Turbine inlet temperature sensed will be signaled to the pack controller which in turn with another sensors signals will control the aircondition system operation.

Ayman Shak'ah
Licensed Aircraft Engineer

A320 Passenger Oxygen System

Dear All,

The A320 has a very nice safe system controlling the passenger oxygen masks. But always please note that we are dealing with machines that you will never get a 100 % efficiency of any machine.

I will brief you little bit about the passenger oxygen masks operation and when they are going to be deployed.

The passenger oxygen masks are installed in PSU - Passenger Service Unit - above each group of seats. This PSU has a door (Panel Which cover the masks container). This door is stay locked electrically by solenoid.

When the solenoid is energized, the door will open and the masks will drop by gravitydown infront of the passenger. The door solenoid is energized by two means.

Either 1) automatically and this is controlled by relays connected to cabin pressure sensor that when heavy drop of pressure is measured at above certain altitude (on A320 above 14000 cabin altitude then this electrical "AND GATE" will make the door solenoid to be energized automatically causing the masks to drop.

2) Manually by the pilot, using a switch that when switched will cause the doors solenoids to be energized so the door will open and the masks will drop.

B.Regards
Ayman Shak'ah
Licensed Aircraft Maint. Engineer

Rules For Dispatching Aircraft For Next Flight

Dear All,

I would like to brief some information regarding the basics in dispatching an aircraft for the next flight. These information are as follow:

1- When the aircraft reached the destination, the pilot will register any comments, faults, warnings, observations,that occured during his flight in the ATL - Aircraft Technical Log Book-. If he has no comment then he will write down "NIL DEFFECTS". At the same time, when the aircraft reaches to the gate, the ground engineer, technician, and or mechanic will carry out walk around, and transit check. Accordingly if he observe any finding such as leak, damage, ...etc he will also report it in the ATL.

2- The Aircraft Log Book is usually has two columns. One for the Finding where to be reported another for the engineer to write down the ACTION TAKEN.

3- There is a book called MMEL "Master Minimum Equipment List" in each aircraft. The MMEL is issued by the manufacturer and approved by the Civil Authorities like FAA, EASA, CAA, ...etc. Note that any airline can make more restrictions to what is mentioned in the MMEL but can't reduce what is already in it. In this case the MMEL will become MEL - Minimum Equipment List-.

4- The MMEL or MEL is the book that has most of the faults mentioned in. It will give the minimum requirment needed for the fault to be dispatched. Like it will mention if this fault is "GO", "NO GO", or "GO IF...". In the MEL also there will be for some faults the code "M" or "O" and or BOTH. The "O" is stated for OPERATIONAL PROCEDURE while the "M" is stated for MAINTENANCE PROCEDURE. That means if this fault occurs then the Pilots have specific procedure to carry out during aircraft operation regarding that system or flight and in "M" case that means the maintenance has procedure to do before dispatching the aircraft. Please note that MEL items are categorized in dispatchable time limitation such as maybe some faults are GO item for maximum limited number of flights another are dispatcheable for maximum number of days and some them are dispatcheable in some atmospheric conditions.

5- The captain can REJECT what the engineer is saying if he felt not convinced in such dispatchable conditions mentioned in the MEL because in some cases he believe in this atmospheric climate condition he may face the next flight as he can see in the meteorology report some troubles. Anyway he can REJECT the action taken and usually in this case this issue will be reported to the MANAGEMENT so they will advice the flight crew what to do or advice the Maintenance personal of what to do. LAST DECISION WILL BE FOR THE PILOTS as they are going to fly this aircraft.

6- there are some faults that you will not find in the MEL. like LEAK. We can find the dispatchable limitation for any leak in the AMM - Aircraft Maintenance Manual - that will state the dispatchable leak limitation and according also to the leak limitation.

7- Some findings maybe like structore damage, in this case the reference will be something called SRM "Structural Repair Manual" that will give the dispatchable measurements of that damage and always we put into consideration if this damage location in pressurized or unpressurized zones on the aircraft.

So far, I hope that this briefing clarify the way of dispatching any aircraft for the next flight. At the end of each aircraft log book page, the ground engineer, or technician, or mechanic will sign certification that the aircraft is safe for the next flight and then the CAPTAIN will sign final acceptance for that aircraft to take.

Best Regards
Ayman Shak'ah
Licensed Aircraft Maint. Engineer