Cessna 310 Fire Hazards from Hot Starts
Entitled "An Augmentor Tube Hazard", the following 1964 Aviation Safety Digest report on a fire to a Cessna 310 is worth studying by pilots currently operating the type.
At Canberra recently, an engine of a Cessna 310 caught fire while it was being started for a flight to Cootamundra. A loud explosion inside the engine nacelle caused the cowlings to be blown open and the fire followed, but it was quickly extinguished by the fire crew and the damage was confined to the cowlings themselves.
At the time the engine was hot and the pilot had at first tried to start it without priming. When the engine would not catch, he primed it for two or three seconds and the explosion occurred on the next start attempt.
Investigation revealed that the aircraft was standing tail into wind at the time and this fact, in combination with the hot and over-primed engine, had allowed the nacelle to fill with fuel vapour. When the engine fired, the exhaust flame in the entrance to the augmentor tubes ignited the vapour inside the nacelle, blowing out the cowlings and starting the fire.
The incident is by no means isolated. In December, 1960, the Digest reproduced a warning issued by the Beech Aircraft Corporation on the dangers of fire when starting augmentor tube equipped aircraft, and in 1961 the Cessna Aircraft Company sent a Service Letter to all operators of Model 310 aircraft setting out the precautions that should be taken against this possibility.
The problem is not confined to Cessna and Beech aircraft but applies equally to the starting of all aircraft that are fitted with augmentor tubes. Pilots can do much to eliminate the problem by at least observing the two golden rules of avoiding engine flooding, especially with a hot engine, and ensuring proper ventilation of the nacelle area by avoiding, as far as possible, downwind or excessive cross-wind start-ups.