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

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

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

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

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