What Happens When the Engines Fail at Cruise Altitude?

I think one reason some air passengers are scared of flying is the idea that if the engine fails, the plane will just drop from the sky. While this is pretty rare these days thanks to aircraft safety systems, backup systems, and pilot training, it can still happen, as shown in the Air Crash Investigation series. So what happens if the engines of an aircraft fail during cruise or mid-flight?

Modern jet engines, including both turbofan and turboprop types, are incredibly reliable. They undergo regular inspections and maintenance and are built to last for thousands of flight hours. But like any machine, they can fail. Engine failures can be catastrophic, either contained or uncontained, and may even lead to a fire. Failures can also be due to component malfunctions that require the crew to shut down an engine mid-flight.

The cruise phase of a flight is the time between climbing and descending. Most of the flight time happens during this phase. Engines are usually not at their maximum thrust during cruise, and failures at this time are rare. But they can happen due to mechanical issues, poor maintenance, or certain atmospheric conditions like high-level ice crystal icing.

Consequences of Engine Failure in Cruise

Loss of Thrust and Altitude

When an engine fails during cruise, several things can happen. First, there’s a loss of thrust. Most commercial planes have two engines, so when one fails, you lose 50% of your thrust. This usually means the plane can’t maintain its planned altitude and will have to descend. Sometimes, especially over high terrain, specific escape routes may be necessary.

Electrical and Hydraulic Issues

An engine failure also means losing the engine-driven generator, affecting the plane’s electrical generation capability. Planes usually have an Auxiliary Power Unit (APU) as a backup. Additionally, the hydraulic pump connected to the failed engine will stop working. Depending on the plane’s design, this could affect multiple hydraulic systems, impacting flight control, landing gear extension, braking systems, and even nose wheel steering.

Pneumatic System Degradation

Engines also supply bleed air to the pneumatic system. When an engine fails, this can affect the plane’s pressurization and ice protection capabilities.

Pilot Response to Engine Failure

Aviate, Navigate, Communicate

If an engine fails during cruise, the priority for pilots is to aviate, navigate, and communicate. First, they must maintain control of the plane, including its attitude and speed. If they can’t maintain altitude, they’ll start descending. Next, they’ll navigate, possibly using a pre-planned escape route to avoid high terrain. Pilots will also communicate the emergency to air traffic control, using standard emergency protocols.

Diversion Decision

After stabilizing the situation, the next focus is on whether to divert the flight. This is a critical safety decision. Many factors come into play, including weather conditions at potential diversion airports, runway length, and available services. Once the decision is made, the cabin crew is briefed, and preparations are made for landing.

No Time for Troubleshooting

You might notice that troubleshooting the engine failure or attempting to restart the engine isn’t a priority. Modern engines rarely fail without a good reason. So, unless the failure was caused by the crew or an identifiable external factor, restarting the engine is usually not advised until after the diversion decision is made.

Last but not least, procedures can be different depending on the airline, aircraft manufacturer, aircraft type, and country’s aviation laws. All the procedures described above are basically general procedures, just to give you a clearer understanding.

In the end, while engine failures are rare, they can happen. Pilots are trained to handle these situations to ensure the safety of everyone on board. Trust your pilots. Their training encompasses almost all possible scenarios, including engine failure at cruise.