Dealing With In-Flight Electrical Fires, Part 1
Editor’s note: This is the first in a three-part series.
One of the worst emergencies most of us can imagine is an engine fire or overheat, occurring just at rotation on a max-weight takeoff. The many iterations of that scenario—such as in the mountains, at night, with solid instrument flight rules (IFR) or others—do little to dispel the concern of actually having this happen to you.
But step back for a moment and consider the engine fire, overheat or bleed duct hot emergency. The pilot knows exactly what is happening. The pilot knows precisely the five or six steps that he or she can take to attempt to fix the problem. Most jets fly fairly well with the loss of an engine, even at high takeoff weights. All the pilot has to do is maintain control of the airplane—in a situation for which it is designed—and return to land.
I flew jets for more than 50 years and I never had an engine fire—with the exception of a blown hydraulic line leaking into hot engine exhaust, compliments of a seven-level North Vietnamese gunner and from which I descended under nylon into the Laotian jungle. Later in my career, I did have one indication, which turned out to be false, of a hot bleed duct. Those were scary in the C-5 world, but we just ran through the steps, shut down the engine and proceeded home.
When confronted with an engine fire, it takes a lot of skill to do exactly what you know must be done. Many factors, such as solid IFR and other complications, can tax a pilot to the limit of their capabilities. The point stands: When an engine is on fire, there is no doubt what is wrong and what must be done to get the plane safely on the ground. Doing it is what requires the skill.
Consider electrics. According to a close instructor friend, insurance claims for electrical problems and fires are 10 times more prevalent than any other emergency. How many things can go wrong and come under the heading of “electrical problem?” How many gremlins can “urinate on the pillars of science” and not be courteous enough to turn on a light and tell us what has gone wrong? These occurrences range from a raging fire on an electrical bus to a frayed wire that renders an instrument unreliable—or shorts out a circuit—but does not warn the pilot.
Here are a few examples.
An airliner experienced a fault with both engine integrated drive generators (IDG) while on approach to Sacramento International Airport (SMF), California. These faults resulted in the loss of electrical power supplied to both electrical networks, leading to the loss of several flight deck displays and systems. Upon the dual loss of power, the ram air turbine (RAT) automatically extended and began driving the emergency generator to provide electrical power to vital services. The airplane landed without further incident and was towed to the gate, where passengers deplaned normally.
A review of the maintenance records found that the testing included a run-up of the engines to check electrical loads per their aircraft maintenance manual (AMM), as well as operational testing of the IDGs. According to the manufacturer, the introduction section of the appropriate troubleshooting manual indicated that if an operator cannot find a fault symptom or fault isolation procedure necessary to ensure the continued airworthiness of the aircraft, the operator should contact them. Unbelievably, this problem had been corrected using what the operator apparently thought was the correct procedures to fix the problem—namely, both generators failing simultaneously. After several more incidents, it was figured that the problem was not the two generators falling offline. The problem was why they fell offline. I admit, dual generator failure would lead me to wonder why—but it is hard to judge not knowing what the maintenance troops were presented with in terms of the actual emergencies.
The National Transportation Safety Board determined that this incident was probably caused by a worn component within each engine IDG, which resulted in the loss of electrical power supplied to several flight deck displays and systems while on approach to landing. The component, a fixed cylinder block, had significant wearing of its reworked brass liners, resulting in the IDGs producing a frequency output outside of their specified design limit.
The second part of this three-part series examines other incidents and causes.