Boeing The purpose of this article is to alert flight crews that commanded engine shutdown may not always be necessary following an engine surge. Depending on whether immediate power reduction has any positive effects, and whether abnormal indications persist, an engine shutdown may not always be necessary.
An engine surge is defined as a power oscillation and/or engine limit exceedance induced by inlet airflow disturbances or internal airflow disturbances inside the engine itself. Some surges are audible, while others may not be audible.
Appropriate flight crew response to engine surge, especially during takeoff, early climb out, and on go-around are especially critical. This article makes observations on some observed undesired flight crew response to engine surge and to suggest desired flight crew response to engine surge encounters.
During engine surge encounters, flight crews are exposed to these potentially high risk errors:
Most undesired crew responses occur in the takeoff and climb phase of flight. However, some have occurred on approach and/or go-around phase of flight as well. Common errors include not correctly identifying the affected engine, not selecting the appropriate Checklist, and/or not accomplishing the checklist as written.
Proper flight crew response to engine surge should be:
Maintain Airplane Control: It is essential that the airplane remains under control at all times during a non-normal engine event; a surge is no different in this regard. It is still recommended that one pilot is responsible for controlling the airplane while the other crew member(s) is directed to address the malfunction.
Analyse the Situation: Non-Normal Checklists should be accomplished only after the malfunction and the malfunctioning engine have been positively identified, preferably after a minimum safe altitude has been reached. Few in-flight non-normal situations require immediate corrective action below a safe altitude.
Malfunction Recognition: The crew-member detecting or recognising the malfunction as an engine surge should announce the malfunction as engine surge and call out the affected engine. The other crew member(s) should independently confirm the malfunction and the affected engine.
Recognition of engine surge should include observation of abnormal engine pressure ratio (EPR) and/or fan speed (N1) values, EPR or N1 oscillations about the commanded setting, differences between engines with equal throttle settings, engine parameter(s) approaching or exceeding limits, abnormal engine noises, and/or no response to thrust lever movement.
While it is common for EGT to increase or exceed limits during a surge, MT rise or exceedance may go unnoticed. Engine surge that occurs at high power settings may include audible popping or loud banging, flames exiting the engine, vibration, and airplane yaw. Sustained engine surge may result in significant engine power loss or failure. Low altitude and high power settings produce the loudest engine surge and the most violent yaw and vibration. High altitude engine surge generally results in a muffled noise, light vibration, and rising EGT.
Some engine surges are recoverable without flight crew action, typically in less than 10 seconds. Some engine surges are recoverable but require the flight crew to reduce power on the affected engine. Some severe engine surges are not recoverable, and surging does not stop even when thrust is reduced. In some cases, surge may stop when thrust is reduced, but resume when thrust is advanced. Persistent EGT exceedance is typically associated with non-recoverable surge and subsequent engine damage.
Checklist Accomplishment: The checklist that addresses engine surge is the ‘ENGINE LIMIT/SURGE/STALL’ checklist. The condition is that the engine indications are abnormal or are approaching or exceeding limits, abnormal engine noises are heard, or there is no response to thrust lever movement. Per the Checklist: Autothrottle is selected OFF/DISENGAGED, followed by retarding the affected thrust lever until indications remain within appropriate limits or until the thrust lever is closed, whichever comes first. If indications are still abnormal and/or EGT exceedance is imminent or persists, then consider placing the fuel control switch to cutoff.
Note that positioning the fuel control switch to cutoff is not a mandatory action in the ‘ENGINE LIMIT/SURGE/STALL’ checklist. The engine may be able to continue running at idle or part power following an engine surge event. To prevent shutting down a good engine by mistake, especially under high workload situations, it is imperative that both pilots confirm the affected engine.
An engine surge may be a startling event and expeditious response to the engine surge is important. However, it is equally important to ensure the correct engine is identified before corrective action is taken, especially if the engine is to be shutdown.
Boeing Flight Operations Review 44, 3rd May 2004