By MR. JAMES BUSBEA, C-5M MFOQA FLIGHT DATA ANALYST
Aviation Safety Action Program (ASAP) #14266 documents an engine flameout and the subsequent “hot start” that was induced by an interruption in the engine shutdown checklist. Like any good ASAP submission, ASAP #14266 provides an opportunity for our community to learn something from another crew’s experience. Hopefully, we can glean some nuggets of wisdom to prevent a similar lapse in checklist discipline or, at the very least, trap the error earlier in the chain of events.
The engine shutdown checklist item at the center of this ASAP is Pilots’ step 8A/Flight Engineer’s step 12A Fuel ISO Valves—“OPEN” (E).
Prior to this step, the engines are suction feeding fuel from their respective main tanks at very low pressure (2–5 psi). The sump box for each outboard main tank is located below the associated engine pylon; therefore, suction feed from these tanks is impossible when the fuel isolation valves are open. So why do we open them?
Each engine-driven fuel pump is mechanically driven by the engine’s high-pressure compressor (N2) and will continue to generate pressure as the engine spools down. We open each fuel isolation valve to provide a path for this pressure to dissipate as the high-pressure fuel shutoff valve is commanded closed at engine shutdown. This procedure prolongs the life of critical engine fuel system components by preventing trapped fuel pressure from exceeding fuel manifold design limits as the engines shut down.
A known risk is that an engine flameout may be induced by prolonged operation with the fuel isolation valves open. Therefore, the engine start switches should be placed to STOP immediately after the fuel isolation valves are opened. In response to ASAP #14266, Air Mobility Command’s Standardization and Evaluation Division bolstered the existing flight manual procedural amplification to further emphasize this hazard.
There is a reason Fuel ISO Valves— “OPEN” (E) was written as a challenge-and-response checklist item. This verbal checklist convention is meant to compel crew coordination between the pilots and the flight engineer. The challenge (i.e., Fuel ISO Valves) announces that the pilots are ready to shut down the engines. The verbal response (i.e., OPEN) not only reports completion of the action but also alerts the pilots that the flight engineer is ready for the next checklist item: Engine Start Switches—“STOP” (P).
Figure 1 shows a normal engine shutdown. No perceptible drop in fuel pressure occurs as the isolation valve is opened because the engine is shut down immediately, as the flight manual prescribes.
Figure 2, on the other hand, shows the engine-shutdown parameters as recorded for the flight in ASAP #14266. The ENG 1 FLAMEOUT caution message displayed about 50 seconds after the fuel pressure decay associated with opening the isolation valve occurred. The Electronic Engine Control (EEC) then automatically transitioned to start mode as soon as the N2 dropped below 61 percent. The subsequent two ENG 1 HUNG START advisory messages and associated fuel flow spikes were indicative of the EEC attempting to restart the fuelstarved engine without starter assistance. When steady fuel pressure was restored by closing the fuel isolation valve with less than 10 percent N2 rotation, a different type of stalled start event—the ENG 1 HOT START—occurred.
Mission complexity, distractions, and external threats are relentless. We ALL succumb to them eventually, and mistakes happen. So how do we contain a lapse in checklist discipline to keep small errors from becoming big ones? First, acknowledge the slipup to yourself and your crew. Then, move forward to correct the mistake as a team. Resist the impulse to reverse your actions or improvise your way out of the situation. Except for boldfaced items, there is never a reason to respond to a caution, warning, or advisory message without direct reference to the checklist. The appropriate crew response for an ENG 1 FLAMEOUT caution while on the ground is to place the engine start switch to STOP.
If you are using ASAP #14266 for a Hangar Fly discussion, take the reported scenario to a logical conclusion. What action is required if fuel flow is observed and the engine does not reach N2 idle? (Answer: Motoring for 30 seconds.) Where is that requirement written? (Answer: Starting engines checklist.) What are the potential consequences if this action is not taken? (Answer: Tailpipe fire.) What would that look like? (Answer: Heavy, dark smoke coming from the tailpipe.) What checklist would you run then? (Answer: Tailpipe fire checklist.)