Smoke in the cockpit could be the result of an electrical fire. The acrid smell of an electrical fire is very distinctive, but any smoke from the area of the instrument panel, circuit breaker panel or any panel with a number of electrical switches should be considered an electrical fire. An electrical fire is a critical emergency.
The Cessna 172 was on a local VFR flight when the pilot squawked 7700 and returned for landing. After landing, the pilot reported smoke in the cockpit and a radio failure.
An RV 7 pilot saw sparks and smoke coming from under the instrument panel. He declared an emergency, shut down the electrical system and returned for landing. After landing, there were no longer any sparks coming from under the instrument panel and the smoke had dissipated. An inspection revealed that a hose clamp had come loose, allowing a metal hose ducting in air from the outside to come in contact with a fuse bus, causing a short.
A Cessna 172R was on a local training flight when the crew noticed smoke and fumes in the cockpit. They declared an emergency, shut down all electrical systems and returned for landing. An inspection by an AME revealed a faulty landing light switch.
An instructor and student in a Cessna 152 were leaving the control zone on a local training flight when both began to smell smoke and noticed a light haze in the cockpit. The instructor then noticed the radio lights begin to flicker. He received a slight electrical shock when he attempted to select the radio to “Off”. The Battery Master Switch was selected “off” and the smoke dissipated rapidly. The instructor then used his cell phone to get clearance to return to the airport and land. He did not declare an emergency. The tower controller did however contact the airport emergency services to stand by. Maintenance personnel discovered that the starter bendix had not disengaged after engine start. The overheated starter caused the aircraft electrical system to overheat, causing the smoke and haze.
Ten minutes after departing from the airport, the Cessna 172 cockpit filled with smoke. The pilot turned the Battery Master Switch “Off” and used his cell phone to declare an emergency and to get clearance to return to the airport for landing. During the return, the pilot reported that the smoke had dissipated, but wanted his emergency status to remain in effect. A maintenance inspection revealed a short from a bare wire.
In the first incident, we don’t know from the report if the pilot shut down his electrical system. All of the other pilots did. From previous aircraft incident/accident reports, we know that people may become incapacitated by electrical smoke in less than 3 minutes. Electrical smoke is toxic. It is imperative to turn the Master Switch “Off” immediately when electrical smoke is detected or suspected.
All of the pilots declared an emergency, either verbally or with the transponder, except the C–152 instructor, and he should have. Fortunately, the tower controller did it for him. You may not know it, but you may be partially incapacitated.
The electrical fire checklist in most aircraft read as follows:
Turn off the battery/alternator master switches.
Don an oxygen mask if one is available.
Turn off all electrical switches.
If the smoke or fire persists, us the fire extinguisher, then ventilate the cabin.
Essential electrics can be selected back on one at a time, while watching for a re-occurrence of the smoke or fire.
“Essential” is a key word here. After an electrical fire, only select “On” those electrical services that are essential for getting the aircraft to the nearest airport. Be prepared to re-select a service back “Off” immediately if the smoke or fire returns.
Trouble shooting to find the source of the fire must be left for the maintenance people with fire trucks standing by, especially if we have used up our one-shot fire extinguisher.
What is essential in an aircraft in VFR conditions? Nothing. The engine will run perfectly well without any electrical services. We can continue to our destination or to an alternate uncontrolled airport and complete a NORDO procedure. If we have a cell phone on board, we can use it to get clearances for control zone entry and for landing as did two of the pilots mentioned above.
In IFR conditions, we may require a radio or navigation aid. We must only turn on what we absolutely require, and then only after some thought as to where the smoke may have come from, and after checking for popped circuit breakers.
Pilots employed in commercial operations are now required to annually review the use of circuit breakers as the result of electrical fires that have occurred when pilots repeatedly pushed in popped circuit breakers. The Transport Canada recommendation and the industry policy is if the electrical system protected by the popped circuit breaker is not necessary for the remainder of the flight, it is not to be reset. If the system is considered to be necessary, one reset is permitted. The breaker is not to be reset if it pops again.
The incidents described above occurred in 2009. Electrical fires do happen. As we can see, following correct procedure will get us home safely in the event we encounter an electrical fire or smoke. Fly safely.
Dale Nielsen is an ex-Armed Forces pilot and aerial photography pilot. He lives in Abbotsford, B.C., and currently flies medevacs from Victoria in a Lear 25. Nielsen is also the author of seven flight training manuals published by Canuck West Holdings.
Got an aviation safety story to tell? Dale Nielsen would like to hear from pilots who have educational aviation experiences to relate. Excerpts from these stories will be used in upcoming safety articles. Dale can be contacted via e-mail: firstname.lastname@example.org.