Do not Wait to Apply the Engine Fire Procedure

An A330 aircraft departed for a long-range flight. The aircraft was in CONF 2 for the takeoff. The takeoff roll was normal, but the ENG 2 FIRE red ECAM alert triggered (T0) 17 s after liftoff. The flight crew continued the climb. The engine display showed stable engine parameters for both engines.

At T0 + 51 s, the aircraft reached 2 400 ft RA. The PF set the engine 2 thrust lever to IDLE and pushed the engine 1 thrust lever to TOGA.

At T0 + 52 s, the PF set the engine 1 thrust lever to MCT and this caused the autothrust to engage in thrust mode.

At T0 + 2 min 27 s, the flight crew set the engine 2 master lever to OFF.

At T0 + 2 min 43 s, the flight crew pressed the ENG FIRE pushbutton and discharged AGENT 1 followed by AGENT 2. The ENG 2 FIRE alert remained after both agents were discharged.

At T0 + 3 min 38 s, the flight crew engaged the autopilot and leveled off the aircraft at 7 000 ft.

At T0 + 6 min 31 s, the flight crew started the APU, which provided the electrical power supply to the right side.

At T0 + 9 min 39 s, the EGT indication for engine 2 started to increase, even though it had shown decreasing EGT from the time when the engine 2 master lever was set to OFF.

At T0 + 10 min 03 s, the ENG 2 FIRE alert stopped and the ENG 2 FIRE DET FAULT amber ECAM alert triggered.

At T0 + 11 min 23 s, the ENG 2 EGT OVERLIMIT amber ECAM alert triggered when engine 2 EGT reached 600 °C.

At T0 + 15 min 09 s, the engine 2 N1 value became invalid.

At T0 + 17 min 35 s, the engine 2 EGT reached a peak value of 801 °C.

At T0 + 25 min 02 s, the aircraft touched down on the runway and safely came to a stop. Smoke and flames coming from engine 2 were seen. The fire brigade arrived and extinguished the fire.

Probable cause identified

Investigation enabled Airbus to conclude that the most probable cause of the engine fire was a leak from the green hydraulic circuit, which may have been due to damage on a green hydraulic line during maintenance.

Delayed application of the fire procedure

Any red ECAM alert requires immediate action by the flight crew to ensure the continued safety of the flight. When the ENG X FIRE alert is triggered, a red LAND ASAP message appears on the ECAM. This requires that the flight crew land as soon as possible at the nearest airport at which a safe landing can be made.

During this event, the engine 2 thrust lever was not set to IDLE until 51s after the ENG 2 FIRE alert was triggered. A further 1m 36s passed (T0 + 2m 27s) before the ENG FIRE procedure was completed to isolate the fire and use the fire extinguishing system.

Nominal engine parameter despite the fire

The engine indications in the cockpit appeared to show that engine 2 operation was normal. This may have been a factor in the flight crew’s decision to delay application of the engine fire procedure.

Remaining fire and further propagation

Analysis showed that the engine fire extinguishing system operated as intended and both extinguisher bottles correctly discharged during the event. It is likely that the fire reignited shortly after extinction due to remaining conditions for fire reignition in the nacelle.

The EGT increased up to 801 °C, which is a sign that the fire spread toward the EGT thermocouples. The fire continued to cause destruction of the fire detection loops and damage to wiring. This was the reason the ENG 2 FIRE ECAM alert stopped and was replaced by the ENG 2 FIRE DET FAULT amber alert. Note that this alert was in the overflow part of the warning display, indicated by a green arrow.

Similarly, the loss of the N1 information was due to damage to wiring.

There are two types of engine fire (fig.1): an engine fire (nacelle fire) and tailpipe fire (internal fire) . Both types of fire affect the engine, but must be treated differently.

(fig.1) Engine fire vs tailpipe fire

Engine fire (nacelle fire)

An engine fire affects the external part of the engine core, but is contained within the engine nacelle. This type of fire can occur on ground or in flight and is usually caused by a malfunction or rupture of a component or pipe, which contains flammable liquids (e.g. fuel, oil, hydraulic fluid). When these liquids come into contact with hot surfaces on the engine case, such as the high pressure compressor, combustor, or turbine, they can self-ignite and cause a fire. This type of engine fire can also be caused by rupture of a part of the engine core causing damage to components and pipes, which can lead to a fire.

The engine fire protection system will detect the fire and trigger the red ENG X FIRE ECAM alert (L ENG FIRE or R ENG FIRE on A220 aircraft). The flight crew must apply the associated engine fire procedure without delay.

Tailpipe fire (internal fire)

A tailpipe fire occurs inside the engine core. This type of fire will only occur during the engine start or shutdown sequence. A tailpipe fire occurs when the engine rotates at a very low speed and residual fuel is present in the combustion chamber or turbine area, or if there is an oil leak in the tailpipe of the engine. The risk of tailpipe fire is higher in the case of a second engine start attempt, because residual fuel may remain in the engine after the first attempted engine start.

The fire detection system does not detect tailpipe fires, because they occur inside the hot sections of the engine core, and therefore, are outside of the fire detection zone. Flight crews can detect tailpipe fires by observing any abnormal increase in EGT during the engine start sequence or if the EGT does not decrease after engine shutdown. Ground crew, cabin crew, or air traffic controllers may also observe a tailpipe fire and must inform the flight crew.

In the case of a tailpipe fire, the flight crew must apply the ENGINE TAILPIPE FIRE abnormal procedure from the QRH. This will ventilate the engine, and the airflow will extinguish the fire and remove any residual fuel or vapor from the engine. On the A220, a tailpipe fire procedure is under study to be introduced in the QRH/FCOM.

After any tailpipe fire, inspection by maintenance is required to check that there is no flame damage to the flaps, wing, or pylon areas.

The detection system for engine fire is composed of dual sensing element loops. They are located in the areas around the engine with the highest fire risk of fire and near compartment air exhausts for overheat detection. These are zones where flammable liquids are present with a potential ignition source, such as the accessory gearbox area, the pylon area above the combustion chamber, the combustion chamber area, and the fan area on certain engines. Each loop is doubled (loop A and loop B) for redundancy purposes. The loops can detect fire or hot air leaks.

The dual sensing element loops are monitored by a Fire Detection Unit (FDU) (A300/A310/A320 family/A330/A340 and A380 aircraft), the Fire Protection Function hosted in CPIOMs J (A350 aircraft), or the Fire Detection and EXtinguishing (FIDEX) Control Unit (A220 aircraft).

Reliability of the engine fire detection system

The design and redundancy of the detection loops ensure a high level of reliability for the engine fire detection system. In the event of an engine fire alert, the flight crew must rely on it.

(fig.2) Example of engine fire detection system on an A320 aircraft with CFM engines

Engine parameters may remain normal during an engine fire

Flight crews must be aware that engine thrust and engine parameters can remain normal in the early stage of an engine fire. The event described in this article is illustrative of this fact.

Apply the engine fire procedure without delay

The architecture of the nacelle is designed to contain the fire threat for a minimum, but also limited time. Therefore, the flight crew must apply the engine fire procedure without delay when there is an engine fire alert.

Timely application of the engine fire procedure will limit fire propagation and prevent further damage to components or pipes around the engine core. Such damage could cause additional leaks of flammable fluids, which could increase the intensity or duration of the fire.

Detection fault and fire propagation

The event described in this article shows how a fire can propagate and damage the fire protection loops, which caused the engine fire warning to stop and be replaced by a fire detection amber fault. As a precaution, the flight crew should interpret a replacement of the ENG X FIRE red alert by an ENG X FIRE DET FAULT amber alert as the sign of a propagating fire. ENG X FIRE can similarly be replaced by both LOOP ENG X LOOP A FAULT and LOOP ENG X LOOP B FAULT on A300-600/A310 aircraft. On A220 aircraft, L ENG FIRE DET FAIL or R R ENG FIRE DET FAIL can replace the L ENG FIRE or R ENG FIRE alert.