Everything that could go wrong with a plane engine — and how a pilot deals with it
One of the most common reasons people have a fear of flying is the worry that something will wrong with the engines. In our everyday lives, we’re used to machines and technology breaking down. Our cars develop a weird clunking noise, our computers lock up and our kitchen appliances go up in smoke.
Understandably, if any of the above events happen we’re not overly concerned, just annoyed at the inconvenience. After all, it’s not like we rely on any of those to get us across oceans.
Generally speaking, modern aircraft engines are so reliable that most pilots go their entire careers without experiencing a major issue.
That said, all pilots know how to deal with just about any engine problem that may occur and all two-engine aircraft are designed to be able to fly safely on just one engine.
Every six months, all pilots practice dealing with engine problems, shutting them down and then landing safely on the remaining engine, all in the comfort of a flight simulator
Should any of these problems happen in the real world we know exactly how to get our passengers back to the ground safely.
Last week, I explained all the indications and information in the flight deck that let pilots know how the engines are performing. Some of the terms used below are explained in that article.
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The phrase "engine failure" is a broad term to cover any number of issues that could go wrong with the engine. In fact, the engine may suffer a problem that doesn’t cause it to fail and we may be able to rectify the issue before it leads to a failure.
Even though it sounds dramatic, by its very nature, an engine is actually always on fire. The burning of fuel in the combustion chamber is indeed a controlled fire. However, if a flammable substance such as fuel, oil or hydraulic fluid comes into contact with hot engine parts outside the combustion chamber, then they can ignite.
With this in mind, the engine has a fire detection system that detects excessive heat in areas of the engine outside of the combustion chamber.
If this system is activated, a fire bell sounds in the flight deck, along with a number of other warnings and indications.
When pilots receive these warnings, they will perform the engine fire drill. This first involves identifying the correct engine that’s encountering a problem. This may seem obvious, but the implications of shutting down the wrong engine could be catastrophic. It’s always better to take a few seconds to confirm the correct engine rather than rushing in and making a huge mistake.
The key part of the engine fire drill is pulling the engine fire handle. This action isolates the engines from the likely causes of the fire — fuel and hydraulics. It also disconnects the engine from the electrical generators that it drives.
The next action the pilots take is to rotate the fire handle, causing one of the two fire extinguishers to discharge into the engine. This is a special gas that displaces oxygen from the engine, starving the fire of one of its key requirements, resulting in the fire being distinguished.
With the fire successfully dealt with and the engine secure, the crew will have to land at the nearest suitable airfield.
An engine surge or stall is one of the most dramatic and alarming events that can happen to an engine as they are normally accompanied by extremely loud bangs, flames from the engine and heavy airframe vibration.
However, the reality of the situation is that the engine is still operating and hasn’t actually failed.
When air enters the engine, it goes through a number of stages where it is compressed down to create maximum energy before it ignites in the combustion chamber. These steps are aided by perfectly engineered blades that direct the air over them and onto the next stage.
If one of these blades is damaged by debris entering the engine, or the blade itself breaks, the airflow stalls meaning that the air cannot be compressed. This will cause a flow reversal of the air already compressed resulting in an immediate loss of engine thrust.
Related: How pilots handle an in-flight engine shutdown
This sudden loss of thrust may be felt in the aircraft by a lurch to one side each time the stall occurs.
To deal with an engine surge, the pilots reduce the engine power until such a point that the surges stop. At this point, they must then decide whether they can safely continue the flight or if they should return to land.
Another event that looks dramatic but actually isn’t that serious is normally indicated by a large flame coming out the back of the engine.
Whereas an engine fire occurs in areas that are not meant to have excessive temperatures, a tailpipe fire occurs in the combustion chamber. As a result, there is little risk to the engine as this area is designed to sustain such heat.
A tailpipe fire can only occur on the ground, usually, during engine start-up, and is caused by excess fuel in the combustion chamber. As this area is designed to be hot, there are no indications in the flight deck that there is a fire. Instead, pilots will most likely be informed by the ground staff, air traffic control or cabin crew.
To deal with a tailpipe fire, we must shut off the flow of fuel into the engine while continuing to keep it turning. This allows air to blow the excess fuel out of the engine, ultimately extinguishing the fire.
Pulling the engine fire handle would actually hinder the process as the action disconnects the engine from the very air needed to help extinguish the fire.
Related: How pilots deal with an engine fire in the climb
The video below shows that, despite how dramatic the event looks, the crew very quickly deals with the issue without any danger to those on board the aircraft.
Severe damage to an engine may be caused by major damage to the fan from birds, debris or a total loss of or damage to a fan, compressor or turbine blade.
The symptoms can be wide-ranging with potential indications coming from any one or several of all the engine parameters. Severe damage could also be diagnosed by heavy vibration or engine surges/stalls.
If severe damage is diagnosed, the safest option is to shut the engine down before any other complications arise.
The actions of the severe damage checklist do the same initial actions of the engine fire drill (disconnecting the engine from the fuel, hydraulics and electric systems) but do not require the use of the extinguisher.
By their very nature, aircraft engines run smoothly when they are spinning smoothly. If anything should impede the rotating parts from doing so, that part of the engine may suffer a seizure.
The most likely part of the engine to seize up is the high-pressure rotor, the N2 stage of the engine. This is normally caused by severe damage to an upstream part of the engine, creating debris that stops the rotating parts from moving.
An N2 reading of 0 is a good indication that the engine has suffered severe damage, requiring shutting down the engine.
The likelihood of an engine actually becoming detached from the aircraft is incredibly rare. However, if there is even a minuscule chance that an event may happen, pilots are prepared for that eventuality.
Even though the event may sound catastrophic, there is very little difference to just shutting the engine down — even though one side of the aircraft will now weigh a few tons heavier than the other. In fact, over time, the imbalance in weight will reduce as only fuel in the opposite wing tank is used to run the remaining engine.
The aircraft will continue to fly normally because the plane's wings provide the lift, not the engines.
Related: Why flying with 2 engines is better than flying with 4
In this scenario, the pilots perform exactly the same actions as if there was severe damage to the engine.
Engine vibration in itself is not a reason to shut an engine down. It's more a cue to monitor the engine more closely as there is obviously something not quite right.
It could be caused by a whole host of reasons including a birdstrike or damage from other debris, compressor blade failure, icing or even just an imbalance in the blades of the engine.
However, just because an engine is showing signs of vibration, it does not mean it is about to fail. If the vibration continues throughout the flight, the pilots will note this in the aircraft technical log so that the engineers can investigate and rectify the problem.
Once an engine is up and running, the combustion process is self-perpetuating. However, if something interrupts this process, such as a lack of fuel, extremely heavy precipitation or volcanic ash, the engine can flame out.
This is most likely to occur in the descent when the engines are at low power, but the aircraft is at high speed.
A flameout may take a crew by surprise as there are no loud bangs or aircraft vibrations associated with the event. In fact, the process of a flameout is much the same as shutting the engine down of our own accord.
As a result, it may take a few moments to notice a flameout as it will only be from noticing a rapid decrease in all engine parameters that will confirm the flameout.
In this situation, pilots have a choice. If there is no obvious damage to the engine, they can consider restarting it. However, if there is any doubt, it will most likely be safer to leave the engine shut down and divert the aircraft than attempt to restart an engine where actual damage has not been spotted.
An aircraft engine, like any other machine, can develop malfunctions. However, due to their importance, they are subject to far greater scrutiny before entering service on the aircraft and then once in service.
Engineers check vital elements such as oil quantity before each flight and the engine even sends a constant stream of data in flight to the manufacturer about the status of the engine.
Despite all this care and attention, if something does still go wrong in flight, the pilots are trained to deal with every eventuality that may occur. From a fire or a flameout to a stall or vibration, pilots practice how to deal with each situation every six months in the safety of a flight simulator.
This means that should a problem be serious enough to require shutting an engine down, the process is done with minimal fuss and stress. The pilots simply apply their training and experience, carry out the procedure and then divert to the nearest suitable airfield.