Electrical Source Fire
When an electrical fire of any kind is noted, or the odor of burning insulation is detected, it becomes desirable to deactivate as many electrical circuits as possible and still be able to fly the airplane and navigate. It is impossible to extinguish an electrical fire until power to that circuit has been severed, and it is for this reason that an “Emergency Power” circuit is provided. In other words, the purpose of “Emergency Power” is NOT to see how many circuits we can keep active, but rather how many we can isolate and do without, until the trouble is found and corrected.
1) Emergency Power Switch - Select to “Emergency” to connect the emergency DC bus (#4) and its components to the batteries and start the small inverter for emergency AC power before turning off all other electrical power.
2) Battery Master Switch - Turn “OFF” to disconnect the batteries from the main bus. This is exceedingly important if the generators are also to be turned off, otherwise the batteries would be supplying all the DC requirements of the airplane. In this case, the batteries would only last approximately three to six minutes. Anytime the generators are turned off, turn off the battery master switch also.
3) Generators - It is necessary to cut power supply to all the bus bars except the emergency bus which is now being supplied by the batteries. Therefore, the generators must be turned OFF to zero the voltage on the rest of the bus bars.
4) Instrument Alternators - In the event this situation should exist for a long period of time it is necessary to guard against the loss of basic attitude instruments. Since the alternators are dependent on engine rotation only to generate AC power for the standby horizon and both turn and bank indicators, select emergency position if deemed necessary or advisable at this time.
The auxiliary gear boxes on engine 1 and 4 each drive an emergency instrument alternator. At 13,600 RPM the output of these alternators is 400 cycles per second. Although this is the desired output for continuous operation, the gyros will operate with any in-flight RPM. On each pilot's instrument panel are two switches dealing with alternators. The 1-2 switch allows selection of #1 or #4 engine alternator output and the emergency switch under the red guard allows the instruments on that pilot's panel to be disconnected from inverter supplied AC power and connected to alternator supplied AC power. Two glow plugs on the First Officer's sill panel, one for #1 engine, and one for #4 engine, indicate that the alternators are producing current but not necessarily all phases. Continued monitoring of these three instruments is necessary to verify normal power. Normally, when all power is lost to these instruments, the gyros will continue to run down slowly and will indicate for a maximum of five minutes with diminishing accuracy. Observing the white flag in the standby horizon will provide a clue to diminishing gyro RPM.
5) Locate the source of the electrical fire and eliminate the defective circuit by turning the switch off or pulling the circuit breaker serving the unit.Then return to normal electrical power by turning on the battery and generators and returning the Emergency Power switch to “NORMAL”. While on “Emergency Power” we can assume approximately thirty minutes of electrical power. In trying to locate the trouble, the following units have caused electrical fires in the past and may be used as a guide in trouble-shooting.
A. Main Inverters
B. Nesa inverters and transformers (transformers located forward of center carry-on luggage rack)
D. Recirculating air fans
E. Temperature control actuating motor
F. Cockpit fans
G. Voltage regulators
H. Hot cup, (due to hostess holding circuit breaker in which had popped out).
I. Jettison system wiring (on test hop for jettison installation).
(Note from TD: the owner of the pilot's handbook jotted down additional items. "Generators" "Short main bus" "Inverters" "Circulating fan")
If radio equipment is determined or suspected as the source, pull all radio circuit breakers except #1 VOR and #1 VHF TRANS. and return to normal electrical power. (Res)et one circuit breaker at a time, in order of preference, until enough equipment (is) operative to operate comfortably or until the defective unit is energized and starts the smoke condition.
If the source of the difficulty cannot be determined and corrected quickly, it (is) important to keep in mind the limited time supply of electrical power and proceed as follows:
A. Land as soon as possible within a thirty minute period on emergency power.
B. If a landing cannot be effected within thirty minutes and battery energy must be conserved until in an area where a landing can be made:
1. Turn on the emergency engine driven alternators to operate the Sperry horizon and bank and turn indicators, return the emergency power switch to “NORMAL” and dead reckon into the landing area. (Remember that when reactivated, the Captain's flux-gate cannot be erected but will correct itself at 4 to 5 degrees per minute.
With batteries and generators off, it should also be remembered that there is no electrical power for the fuel booster pumps. At low altitudes, this provides no problem, but at higher altitudes, nose high attitudes, steep banks, and uncoordinated maneuvers should be avoided so as not to disturb the gravity feed of fuel to the engines. If an engine should flame out while in this configuration, it cannot be restarted unless at least one generator is turned on to provide ignition and this may very well rekindle the fire since ALL electrical circuits would be reactivated.
When landing on emergency power it is recommended that a generator be turned on momentarily to check for three green gear lights and repeated upon touch down to remove the prop locks to secure ground fine pitch for braking.
No written procedure can possibly cover all factors in emergencies in flight. If conditions permit a search for the fire source immediately after going to emergency power, it would be to everyone's advantage if the defective unit is isolated and the trip completed as planned. Remember that the emergency power circuit is designed to allow operation on as little as is practicable and not to operate on as much as is possible with the power remaining.
From past experience electrical fires have seldom produced more than smoke while a motor or other unit is overheated. If nothing is done to correct the situation the unit usually shorts out and then pops a circuit breaker or blows a fuse, or the wires in the unit burn through and open the circuit so all current flow stops. Motors are usually mounted in brackets away from flammable parts and often go undetected when they “burn out” as the saying goes. Such is the case with units such as spill valve actuators in the wing, generators or feathering pump motors at times.
With this is mind, while operating on emergency electrical power, if the situation is such that you do not understand or are confused, do not hesitate to return to normal electrical power in order to re-orientate yourself or positively check a system in order to enhance the safety of the operation. If you had to make an ILS approach under these conditions, reactivating the entire electrical system for the approach might be far less hazardous than attempting an approach with VOR receiver only.
This discussion is not intended to minimize the electrical fire hazard, but to point out alternative actions which under certain conditions would result in a safer handling of an emergency situation.
(End of Section 2 Part 10 of Viscount Pilot's handbook)
The CAB accident report for United Flight 823, Page 14, states: “The only source of overtemperature in this compartment (electrical bay) is a gross electrical fault to ground. The emergency procedure executed by the crew does not support a gross electrical system malfunction. An electrical source smoke or fire emergency is combated by turning the emergency power switch on and placing the battery master switch and generators off. Equipment that was operating at impact and DME operation to five miles before impact shows this particular emergency procedure had not been executed.”
There are several instances in the above notes dealing with an electrical fire that give suggestions as to when the Captain could have returned to normal electrical power.
1) Normal electrical power can resume after a shorted circuit is found and the breaker pulled or otherwise disconnected.
2) If radio equipment is suspected to be a problem, all radio breakers should be pulled one breaker at a time- with the exception of #1 VOR and #1 VHF Transmitter. Once accomplished, it is suggested that the captain may return to normal electrical power.
3) It is also suggested that, in the event of the pilot being confused, a return to normal electrical power can be done in order to “re-orientate” himself and to positively check a system.
The Civil Aeronautics Board's conclusion does not offer consideration that the pilot may have already performed trouble-shooting before returning to the normal electrical power settings that were found by crash site investigators.
It should also be noted that the CAB accident report, on Page 8, states that “…two VHF radio transmitter selection switches were positioned on “No. 1 VHF Com”. The No. 1 VOR navigation receiver was tuned to the Knoxville VORTAC…“ These are the two breakers that WERE NOT to be pulled by the pilot in the event of an emergency electrical situation-if radios were suspected as a problem source. (See boldface above).
Also in boldface above: “With batteries and generators off, it should also be remembered that there is no electrical power for the fuel booster pumps. At low altitudes, this provides no problem, but at higher altitudes, nose high attitudes, steep banks, and uncoordinated maneuvers should be avoided so as not to disturb the gravity feed of fuel to the engines.
It is common knowledge that United Flight 823 was flying for its last several minutes at extremely low altitudes.