JohnBurke

To "turn off the engine?" Do you mean to retard thrust levers and cut off fuel while arming or activating fire switches or T-handles to cut off bleed, electricity, oil, fuel, and hydraulics and arm the fire bottles?

I have never heard of a procedure involving making turns to see if there's "smoke behind."

The reason that we have fire detection on an engine is because we may have no other indications.

Most engines utilize at least two fire loops, and include both fire and fault logic to aid in discriminating between a fire and a loop fault. There are various reasons for a high temperature in an engine nacelle or pylon area, which could be an actual fire, a bleed leak, etc. Accordingly, fire loops use logic to look not only at a given temperature, but a temperature rise, comparing the indications of both loops, the differences, if any, the time to reach a fire indication, and so forth. Most systems will identify a fault based on certain types of logic and use that to provide a valid fire or fault indication in the cockpit.

Swissair 111, a MD-11 is a good example of a crew that didn't take the fire indication seriously. It didn't involve an engine, but a fire which developed as the result of an onboard entertainment system. The crew could have landed the aircraft, but elected to fly over the water, away from the airport, to dump fuel and set up for the approach. Everyone died. It turned out to be the worst air disaster Canada has seen.

UPS 6 was close to Doha when a lithium fire developed on the main cargo deck of the B747-400. Rather than land in Qatar, they elected to attempt a return to Dubai, and crashed in the desert. These, and numerous other mishaps point to a very grave reason that we take fire warnings seriously. If we respond appropriately to a fire warning and it does turn out to be a false alarm, we can consider the old adage that it's far better to be on the ground, wishing you were in the air, than in the air, wishing you were on the ground.

In the older A model C-130's we had photo cells in the nacelles as fire sensors, and those could be activated by sunlight or a bright reflection from the ground, into the nacelle; I have had occasion when receiving a fire indication to make a 90 degree turn to change the angle of light into the nacelle, and noted the fire indication went out.

Having said that, if we get a fire indication and it goes away, we may have just seen our fire detection destroyed by fire...that doesn't mean it's a good time to call it a false alarm and press on. A valid fire indication with a memory procedure is not the time to play second guess. We do not attempt to turn and look for a smoke trail. That would be idiotic. We do not attempt to go look at the engine to see if t's really on fire. We follow the procedure for an engine fire, wheel well fire, lav fire, etc.

Some aircraft systems may show an overheat, rather than a fire, which is most often a bleed leak, and will involve shutting off bleed air, reducing power, and other steps to detemine the source and to stop the overheat condition.

To receive a fire indication and attempt to second guess it by making the dangerous assumption that it's a "false alarm" is to quite literally play with fire. Given that a fire can double in size every 60 seconds or less, one may not have much time. Steps involved in fire procedures including removing or limiting the source of the fire, such as cutting off fuel, oil, hydraulics, bleed air, and electricity. Steps may include discharge of fire agent, depressurizing or stopping airflow to a compartment, etc. Over the years, I've experienced wheel well fires, brake fires, cabin fires, engine fires, lav fires, cockpit fires, and other fires on board in flight, and indications that appeared to be a fire, but were not. It's my considered opinion that an attempt to down play and ignore or second guess procedures and fire indications is a bloody idiotic thing to do, and quite possibly one of the last idiotic things one may ever do.

Some years ago I entered a shop one morning to find an engine being removed from an aircraft. The owner was angry that the crew had discharged fire bottles and scrubbed a flight the night before. It took only a moment to find evidence of a fire, as well as a catastrophic engine failure. I found engine pieces imbedded in the floor inside the aircraft. The owner had chewed on the crew, claiming they responded to a false fire indication. The crew followed their procedure, blew both the bottles, and landed ASAP. Everyone got out, everyone survived. The crew was right, the owner wrong.

Bottom line, when you're the pilot in command, the owner, operator, director of operations, director of maintenance, customer, FAA, president of the united states, bishop, pastor, or witch doctor, will always have less authority than you. As the pilot in command, yours is the final authority, and the owner/operator/DO/DoM/FAA/MIC/KEY/MOUSE is on the ground, where it's safe. You're not. You're responsible for that aircraft, it's contents, its safe conduct, and for adhering to the procedures developed for that aircraft. Who gives a damn if it's a false indication? If you follow the correct procedure and it turns out to be a false indication, that's a maintenance issue, but you're not there to build the airplane, or work on it. You're there to see that the aircraft is legally and safely operated. Period. End of story. Let someone else figure out if it was a false alarm, later, on their time. That's not your concern. Follow the procedure, act in the conservative, safe interest of the flight, and leave the second guessing to others who have that luxury, on the ground.