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"In the unlikely event that..."



You may often hear the term, “in the unlikely event that…”, while flying on an airliner. This may bother you, particularly if you tend to be a nervous traveller. What this tells you, is that most of the likely scenarios have been considered. Not merely considered, but planned for, trained accordingly and the crew evaluated in a simulator and found to deliver a high standard of performance. Part of this training is designed to brief passengers on certain procedures, to make the execution of the procedures that much simpler.

When I mentioned the word “most” of the likely scenarios, it means that the crew is trained for all of the major and minor problems. As in life, it is not possible to predict all eventualities. Pilots are trained to be equipped with a set of skills to help identify and take necessary action for all eventualities. Please be assured, the crew you are flying with on commercial airlines, are highly trained and highly competent. They are required to demonstrate their ability every six months. This proficiency check has technical, procedural, flying and interpersonal aspects. It takes place over two days, with classroom discussion and simulator work on each day. The required minimum is also set by the regulating authority, but as is often the case in airline operations, a more stringent requirement is set by the airline. This ensures the standard remains very high.

So how does this training look? About six weeks before day one in the simulator, most pilots start their preparation. The training department delivers the training material well in advance. Every six-monthly cycle covers a few major topics on the technical aspects of the aircraft including: fuel, hydraulics, air systems, landing gear, navigation systems, engines, fire protection… One or two of these topics will be addressed, with particular attention to something that has recently happened worldwide, or has become a concern within the airline.

The most recent training I have attended included hydraulics. I read all the content available on hydraulics. This includes the basic normal operations, such as maximum and minimum quantity levels, normal pressure limits, interrelationships between system A system B and the standby hydraulic reservoir. After reading normal operations, I review my flight crew training manual. There may be some technique described in how to conduct a transfer of hydraulic fluid from system A to system B. This is not done on a day to day basis.

Next I review the schematics of the hydraulic system. This helps me visualise the systems that makes use of hydraulics and how they fit together. As an example, raising and lowering the landing gear makes use of hydraulics. So do the flight controls. The ground spoilers, which are big panels that pop up on top of the wing on landing, also make use of hydraulics. Ground spoilers destroy lift going over the wing, which assists in settling the aircraft firmly on the wheels for traction. They also add aerodynamic drag to slow the landing roll. Wheel brakes also use hydraulics. The schematic of the landing gear, flight controls, ground spoilers and brakes in a closed loop circuit of hydraulics gives me a visual repersentation of the system. All critical items are backed up an additional standby hydraulic system.

Now that I have a good understanding of the hydraulic systems, I will read in more detail about potential anomalies in the system. This explains the meaning of the warning lights. It will also tell me how the light is triggered. When system A is below a certain quantity, the Hydraulics System A warning light will illuminate. The Flight Crew Operations Manual guides me through the back-up systems. This manual specifies which systems will be lost in the event of a hydraulic failure.

I am nearly complete with my reading on the hydraulics system. The minimum equipment list, is the source that indicates whether a flight may depart or not. It lists all defects where a technical intervention allows the flight to continue. It describes the specific conditions in which we may depart. The MEL also shows how to adjust our operations accordingly.

Finally, I look at the quick reference handbook. Pilots consult this book first when there is trouble. This book guides me through a hydraulic failure whilst in the air. First I locate the chapter on hydraulics. Next I look for the sub-heading which closely matches my situation. I then turn to that page and confirm all the indications and warning lights are the same. The lights, sounds and warnings indicate hydraulic "system A" has failed. Check. Now there is a checklist to guide me in isolating hydraulic "system A". We are unsure of what caused the failure, so we isolate the system to prevent further damage.

But there is always a catch. We have isolated system A. How does that now affect us on our flight to Cape Town? Which systems were fed from system A and which were fed from system B? Do the ground spoilers operate on the standby hydraulic system? That’s the reason I spend time reading as much as I can on the technical chapter for this cycle.

During the debrief, we discovered our scenario today, was that a strip of rubber had been flung up from the wheels during the take off roll. This caused damaged to the hydraulic lines in the landing gear bay. The damage was not contained by isolating system A. It also affected the standby hydraulic system. Now we are in a serious emergency. We only have one hydraulic system left and need to land as soon as possible.

The damage occurred on take off. We were alerted within minutes, but we spent an hour assessing and actioning our emergency. We completed all the appropriate checklists and read up on our new landing performance, without brakes and spoilers. The runway was long enough for us to return. We landed back safely. I now know that should I have any hydraulic problem in the future, I have seen how it plays out. I am comfortable to announce that you are in safe hands.


Alex MacPhail

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