Aircraft Deicing

Winter is coming, the formation of ice on top of the wing either during flight in cold area or after aircraft parked overnight in cold weather can alter the aerodynamic of the wing which can effect the lift force during take off.

To removed the ice & prevent it from reoccur, deicing fluid will be used which normally will be performed by well trained deicing team.

The commonly used fluid is either of ethylene glycol or propylene glycol however the latter is more common due to the fact it is less toxic.


Deicing fluid can be devided into 4 different type, type I, II, III & IV. Type II fluids are more commonly used and have thickening agent to prevent their immediate flow off aircraft surfaces. Typically the fluid film will remain in place until the aircraft attains 100 knots or so, at which point the viscosity breaks down due to sheer stress. The high speeds required for viscosity breakdown means that this type of fluid is useful only for larger aircraft.

Poor Maintenance Practices

I've found this while removing the right hand heat exchangers for cleaning. The clamp was"sitting" on top of the pneumatic duct.

It is posible that the ducts have been removed & reinstalled back with the top duct been normalised first, the lower duct then was reinstalled without the mechanic that done the installation aware of the contact.

All pneumatic, hydraulic, flight control cable must be inspected for interference with adjacent structures to eliminate unnecessary defect in the future. In the case above, due to vibration, crack can occur which will lead to pneumatic leakage and subsequent damage.

Refueling Control Panel

This is the place where control for refueling process took place. Located at the forward edge of right hand lower surfaces. Amount of fuel required base on the flight plan will be routed to certain tanks by controlling the switch of each tank. What unique about BBJ is that, there is additional control for auxiliary fuel tank which is located in forward and aft cargo compartment.

Normally the wing tank will be filled up first followed by the center tank, any extra fuel required then will be routed to the auxilliary tank. Depend on the density of the fuel for that day (fuel density varies mainly due to temperature) the maximum quantity for each wing tank is 3800 kg (4800 liters) and center tank 12750 kg (16200 liters). For auxilliary tank, on BBJ that i work on it has 1 auxiliary tank at the forward cargo and 3 tank in the aft cargo, each can be filled up to 1500 kg (1900 liters) and 2900 kg (3600 liters) respectively.

In each tank there is an instrument that will measure the capacitance of the fuel and from that through fuel processing unit will convert it to kilogram. Weight of the fuel is more relevant for aircraft as it will be added to total weight of an aircraft to determine take off thrust setting for engine for that particular flight.

Cockpit Window Cracked

One of our BBJ aircraft came back with number 2 cockpit window cracked. No 2 window is the only window that can be opened, it slide backward. This is very dangerous situation where it might lead to rapid decompression however by knowing the construction of the window itself, we can be assured that the safety is not tolerated.






This window is a laminated assembly of layers of glass and vinyl or urethane. The structural inner glass pane carries pressure loads. The vinyl interlayer is structural for bird impact resistance and fail-safe pressure loads.

The current window manufactured by PPG has these layers: an non-structural outer glass pane, a non-structural urethane interlayer, a structural vinyl interlayer, a non-structural urethane interlayer and an structural inner glass pane.

A conductive film is located on the inner surface of the outer glass pane, which is a part of the window heat system that supplies the anti-fog and the anti-ice function.

Rest of the cockpit window have almost the same construction. The passanger window however in stuuctured in layers as well minus the heating element.

Few months earlier one of our Gulfstream had a similar incident where the number 1 cockpit window cracked during flight, from the sign of arcing at the top left corner of the window, overheated is the probable caused for the damaged.

Heat Exchanger Cleaning

Summer already started and ambient temperature is now getting higher and higher everyday until September when it will start to drop again.

In hot weather like this, the airconditioning system (a/c) will have to work harder in order to produce sufficient cool air to chill out the cabin. The heat exchanger is part of airconditioning system where transfer of heat from the engine bleed air back to ambient before the air further process by the air cycle machine (heart of a/c system) to produce cool air.

With dusty enviroment such as here in middle east, the dust or dirt can accumulate in between the fins of the heat exchanger thus reduce the efficiency. Cleaning of the heat exchanger is necessary, with heat exchanger backfush cleaning process.

Here is the photo that i took while we doing it on one of the BBJ, the mix of hot air and water was injected from backside of the heat exchanger so it force out the dust and dirt that trapped inside the heat exchanger itself.

There is slight improvement for the output of the a/c system after we did this, however with ambient temperature of 45 deg C, getting sufficient cool air out of the a/c is seems difficult, we still need the use external ground airconditioning cart.  

How To Change Aircraft Wheel

Ever wonder how the replacement of aircraft wheel been done? With big in size and heavy in weight, without special tools it will be imposible to be done. Here is the general description of it so that all of us have some ideas how it is done.

Depend on the organisation, in the company that currently i work with, we had a wheel change trolley where the new wheel is placed as well as the nitrogen bottle needed to charge the wheel.

Aircrat will be jacked from the axle to raised it up from the ground, then one and only nut that hold the entire wheel will be loosen and unserviceable wheel ready to be removed by sliding it out from the axle.

With the wheel dolly, which can be raised and lowered, the weight of the wheel will be supported and the wheel will be slide out from the axle, later on the new wheel be placed on the dolly and slide back to the axle.

The big nut again will be tightened and torqued to certain level to ensure proper sitting of the bearing sof the wheel, then it will loosen again and final tightening at lower torque to secure the wheel.

Take note that on B737 BBJ, the only thing that hold the wheel is this big nut on the left, however this big nut is secured by two extra bolt to prevent it getting loose during operation.

Pre Refueling - Water Check

Prior to carry out refueling of an aircraft, the quality of the fuel from the fuel truck (bowser) must be checked to ensure it cleanliness as well as the present of water. Dirty fuel can caused fuel filter clogged and water can frezzed at high altitude during flight thus blocking the fuel going to the engine.

Normally at the bowser, there a small glass container in which fuel sample from the bowser can be collected. Visually we can check the cleanliness. To check for presence of water, we need to use the water detector capsule.

With water detection capsule attached at the front of the shringe, the fuel that been suck will pass through it. The capsule contain chemical that will change colour when exposed to water molecule.

If no water molecule present in the fuel, the capsule colour will remain unchanged from the original which light yellow.

This is what happen when the water introduced to the capsule. Turned dark blue which indicate the present of water.

So far i never had an experience this test failed from most of the fuel supplier around the world, aircraft fuel is high quality kerosene that been processed through very strict high quality standard to ensure safety operation of an aircraft.

Thanks to Benny from Cotonou, Benin which coorperate & enable me to take the photo of the test.

My New Blogs

From now on i will on ly post technical information in this blog, posting about my experience, fun and joyful article will be in the following blog.

http://dutytravel.blogspot.com

For those who had asked questions to me in a past, i post the questions and answers in this blog.

http://askengineerhelmi.blogspot.com

Enjoy..

Most Eventfull Flight - Morrocco - Benin - Angola - Libya

I just came back from the most "eventful" flight as quoted by maintenance controller to whom we consult incase of defect during line operation.

From Abu Dhabi to Al-Ain, landed with Air Traffic Controller no 2 failed, while fueling the fuel to Rabat, the fuel automatic cut-off once the center tank reach it maximum level also failed thus overflow from the underwing fuel tank vent outlet.

From Rabat, we go to Cotonou, Benin, then to Luanda, Angola and back to Cotonou. Then we go to Tripoli, Libya, on departure back to Cotonou we have Auxilliary Power Unit automatic shutdown, interrogate APU BITE (Built In Test Equipment) found autoshutdown due to high oil temperature, we departed with engine start using ground air starter. Before start there is CDS (Common Display Unit) fault messages, cycle the circuit breakers clear the defect.

Landed safely in Cotonou and opened APU cowl to check any abnormalities, found APU oil scavenge filter pop-out indicates filter is clogged, APU remained inoperative and will be repaired once aircraft returned back to base.

On departure back to Abu Dhabi, IRS (Initertial Reference System) ON DC fault light came on, found IRS circuit breaker pop-out, reset back and after 5 minutes IRS fault cleared, then we have both engine control ALT fault and TCAS came on as well, recycle ENG control switch & TCAS circuit breaker cleared both defects. I'm sure all this avionic defect related to less cooling as we dont have airconditioning during aircraft preparation as the APU is inoperative, as it get hot, the electronic units tend to failed and trip off to prevent further damaged.

I'm preparing this write-up from 37000 feet on the way back to base, long 8 days trip and of course with full of experience. From Africa with love.......

Key To Start An Aircraft Engine.

Is there any key to start an engine? The answer is no. The only thing that is required to start the engine is to turn the start switch knob, here is the pic of the knob so that you can figure out how it is looks like.

As an aircraft engineer, from time to time we do need to start the engines to check their performances or perform leak checks after the maintenance task has been performed.

After preparation have been made in term of other aircraft systems such as pneumatic, hydraulic & electric, plus after safety measures have been comply with, the knob will be turn to GND position. This will direct the pressurised air from pneumatic system to the aircraft starter that which, through the gearboxes will turn the engine, after certain percentage of engine rotation, the fuel will be introduced that will direct the fuel to the combustion chamber plus the ignition will be light-up at the same time. Here is the pic of the fuel lever for both engines.

As the combustion happen inside the engine, the starter will automatic cut-off by the computer including the ignition, not like in car engines where ignition happen all the time as the piston goes up and down.

Once the engine stabilize at idle then the whole process of starting is completed, the same sequence applied to the other engine.

Auxilliary Fuel Tank

BBJ (Boeing Business Jet) can travel longer range compared to conventional 737 due to this extra fuel tank added in its cargo hold.

Depend on certain configuration per customer specific need, this extra tank can be placed at aft area of the forward cargo or forward area of aft cargo hold. This is to ensure center of gravity of the aircraft remain close to the center of the aircraft.

Each tank can hold around 1800 liters of fuel which if converted to kilograms will be around 1500 kg except the master tank which will have much higher capacity.

All fuel from auxiliary tank will be routed to the center tank of the aircraft before goes to the engines. What unique about this system is, fuel from auxiliary tank is "pump" to center tank using differential pressure from the cabin which will start once fuel in center tank dropped to certain level.

During initial refueling before the flight, the fuel will be added to the wing & center tank fuel first, extra fuel required for the flight then will be filled up in this auxiliary tank.

It's hard to see how this aux tank looks like, i found this extra tank kept in the store, it has been removed form one of the BBJ due extra cargo space required for the baggage. if you need extra range for the distance, cargo space has to be sacrifice for the fuel tank...

CFM Engine Using BioFuel

BBJ is using CFM56-27 engine for it propulsion system, what i want to highlight here is in June 2007, the engine manufacturer CFM International has successfully carried out an initial test of a CFM56-7B engine using an ester-type biofuel at Snecma’s Villaroche facility near Paris.

CFM56 engines are produced by CFM International (CFM), a 50/50 joint company of Snecma (SAFRAN Group) and General Electric Company.

The biofuel used for this test is 30 % vegetable oil methyl ester blended with 70 % conventional Jet-A1 fuel. This test was designed to check the operation of a jet engine using a fuel made from biomass, without making any technical changes to the engine. With this type of biofuel, the target is a net reduction of 20 percent in carbon dioxide (CO2) emissions compared with current fuels.

CFM is running engine tests to develop solutions based on mixtures of jet fuel and second-generation biofuels. For instance, it is currently focusing on the evaluation of alternative fuels made using biomass (offering properties closer to those of jet fuel), which also offer better environmental performance.

For alternative fuels to be used in the aviation industry, there are a number of major technology challenges that must be met, including energy density, thermal stability (avoiding coking at high temperature), use at very low temperatures (freezing) or high temperatures, lubricating effect with materials used, and the availability of mass production facilities worldwide.

Even though it is only 30% "vegetable oil" as a start, it is a major step toward greener emission from aviation industry.