Can a passenger jet fly with only one engine?
A twin-engine plane can fly perfectly well on only one engine. In fact, it can even continue the take-off and then safely land with just one engine. An engine failing in flight is not usually a serious problem and the pilots are given extensive training to deal with such a situation.
What do the pilots do if an engine fails?
All pilots are taught to abide by a basic aviation rule regardless of the severity of any airborne event. This is summarised by the acronym; Aviate, Navigate, Communicate. The crux of this is to ensure the flight crew prioritise flying the aircraft first. This is ensuring that it is fully under control before verifying or correcting its navigational path and making sure it is flying where the pilots want it to fly, i.e. not heading towards a high mountain. This is followed by communicating the relevant information to all the appropriate parties, starting with Air Traffic Control.
There are several different severities of engine problems that might require slightly different responses from the flight crew, defined by the level of urgency. For example, if an engine fire is indicated, this requires an immediate response after ensuring the aircraft is under control (‘Aviating’!). If for example, there was an engine fire indication, there are several ‘Memory Actions’ for the flight crew to complete. This will involve completing the engine shutting down, and subsequently deploying the fire extinguishers from memory, without the aid of a checklist.
Once the engine is shutdown…
Once the engine is safely shutdown and the fire extinguished, the crew would reference that the ‘Engine Fire Memory Actions’ had been completed correctly by referencing the appropriate checklist. The checklist will then detail further tasks for the crew to complete that were not included in the ‘Memory Actions’.
On the other hand, if it was a straight forward engine failure with no damage indicated, there would be no ‘Memory Actions’. In this case, the pilots would follow a checklist to diagnose and potentially restart the engine. Any engine failure on a twin-engine aircraft will require the pilots to land the aircraft at the nearest suitable airport. Statistically this is unlikely to be your destination unfortunately!
‘Memory Actions’ for an Engine Fire or Severe Damage
Different types of aircraft may have different names for the various switches, handles and procedures, but the basic principle remains the same; to safely shut down and secure the engine in a timely manner. These steps are typically as follows:
- Disengage the Autothrottle – this stops automatic thrust control.
- Reduce the thrust on the damaged engine to idle – this involves moving the respective thrust lever all the way back to its idle position.
- Fuel control switch to off – this closes the fuel valve, stopping fuel flow to the engine.
- Pull the fire handle switch – this typically disengages the electrical, hydraulic, pneumatic and fuel systems from the respective engine.
- If a fire is still indicated in the engine, turn the engine fire handle to discharge the first fire bottle. After waiting around thirty seconds, if fire indications are still present turn the fire handle the other way to discharge the second fire bottle.
Each of these actions MUST be verified by both crew members. For example, the pilot completing the checklist will touch the respective control switch, such as the Fuel Control Switch, and the other pilot will confirm they are about to action the correct switch prior to moving it. It is required to be completed at a reasonable pace (not rushing through) to ensure the wrong engine is not shutdown.
The engines are designed to contain any fire within it’s housing to stop it spreading to any other part of the aircraft. However, if an engine fire continues after this procedure has been followed, the flight crew may need to consider an immediate landing. In very severe cases, this may mean a forced landing away from any airport (i.e. in a field or suitable area). However, rest assured, the potential of such an occurrence is unbelievably remote.
Reasons why an engine might fail or be shut down by the pilots:
- Severe Damage (for example a turbine/fan blade separation or bird strike)
- Separation from the aircraft
- Stall (an engine stall is different to the aircraft wing stalling)
- Fuel Starvation or Contamination
- Flame Out
- High vibration
- Limitations exceeded (too hot for example)
What are the implications of an engine failure?
Asymmetric Thrust / Controllability
The first implication is the asymmetric thrust that will be produced. If an engine fails and is shutdown, the other engine’s thrust is increased to stop a decay in airspeed. This results in the aircraft wanting to turn away from the working engine and entering a turn. If left unchecked, this will result in loss of control of the aircraft. This usually has to be corrected manually by the pilots through the rudder pedals. Any time there is an adjustment in speed, thrust or altitude, the pilots will need to ensure the aircraft remains balanced and in control.
With 50% of the aircraft’s power no longer available it will not be able to maintain its cruise altitude. If the aircraft is in the cruise at the time of the failure (which is statistically most likely), a descent will need to be quickly initiated to an intermediate altitude which can be maintained by the remaining engine (typically between 15,000ft – 25,000ft for most aircraft, depending on weight).
Many of the aircraft’s systems are powered by its engines. These usually include the Hydraulics, Pneumatics (which provide cabin air) and Electrics. Whilst these systems have a level of redundancy (in part through the other engine), some parts of the system may no longer be available which could affect aircraft handling and performance.
Losing an engine often requires a different flap configuration for landing, in part due to the performance that must be achieved were the aircraft to abort the approach/landing and conduct a ‘go-around’. Landing with a lower flap configuration increases the landing distance required and therefore the pilots must carefully consider which airport they elect to land at. Airport weather, runway length and aircraft weight all play a part in these considerations.
What is the most dangerous phase of flight to have an engine failure?
For a pilot, the most testing place to have an engine failure is during the take-off phase, i.e. the start of the ground roll until the aircraft passes around 1,500ft. However extensive training is provided for this scenario and the pilots are tested on their reactions to such an event every six-months in the simulator. They must safely deal with such a scenario to a high standard or they will not be allowed to continue to fly until adequate performance is demonstrated.
During the take-off, the pilots use a carefully pre-calculated speed called V1 (pronounced “Vee One”) to determine their actions were an engine to fail. During the take-off roll, if an engine failure occurs before the V1 speed, the pilots must abort the take-off, which is known in the industry as a ‘Rejected Take-Off’ or RTO for short. If they elected to continue, the aircraft would not gain enough speed to take-off with the remaining engine power available on the runway length remaining.
Continuing the take-off
If a failure occurs after V1, the pilots must continue the take-off and get airborne. If the pilots tried to abort the take-off at this speed, there would not be enough runway left to safely bring the aircraft to a stop.
Once the aircraft is in the air, the pilots will just concentrate on flying and controlling the aircraft until approximately 400ft. At this altitude, they will review what has occurred and carry out any ‘Memory Actions’ if required.
What happens if you lose an engine on an aircraft with more than two engines?
A four-engine aircraft losing a single engine is even less of an issue. A few years ago, a four-engine Virgin Atlantic Boeing 747-400 (a jumbo jet) had an engine failure over the United States en-route to the UK. The aircraft continued all the way over the Atlantic Ocean back to the UK without any further problems.
If a four-engine aircraft lost more than one engine, it can still potentially fly at a lower altitude and will perform better at lower weights.
What is the likelihood of an engine failure?
With the significant technological improvements that have occurred over the last few decades, engines are built to an incredibly high standard and are very robust as a result. Over the last few decades, engines failures have become increasing rare to the point that the majority of pilots will now only see an engine failure in the simulator over the course of their career.
Safety statistics suggest that less than one in every one million flights will have an engine failure or forced engine shutdown in the air or on the ground. This works out at approximately 25 such failures a year across commercial aviation.
If a failure does occur, the engine is designed to contain any problems and stop it spreading to the rest of the aircraft. For example, if one of the fan blades at the front of the aircraft detaches, the engine casing should stop it leaving the engine.