Debrief


Fuel Tank Selector Reminder

On March 19, 2006, an amphibious Cessna A185F lost all engine power shortly after takeoff. The pilot was able to land on the remaining runway, but the landing gear could not extend fully, causing minor damage to the keel strips. Prior to starting the engine, the pilot rotated the fuel tank selector into what appeared to be the BOTH position. After starting, the engine was operated at idle until the oil warmed up to 75° before a run-up check was performed. The aircraft was then taxied a short distance to the runway for takeoff. When the engine lost power, it had been running for 10 to 12 min. It was determined that the fuel tank selector was in an unmarked OFF position; 180° opposite the BOTH valve to an accumulator tank mounted on the firewall, thence through a fuel shut-off valve into the engine compartment. The fuel tank selector valve is located on the cabin floor between the front seats. There is a vapour return line that returns vapour and excess fuel from the engine-driven fuel pump to the accumulator tank.

The valve is described in the pilot operating handbook (POH) as a "three-position selector valve labelled LEFT TANK, RIGHT TANK, and BOTH ON." When not installed, the valve can be rotated to a fourth position, OFF, that is 180° opposite the BOTH position. The valve has detents that have the same tactile feel in all four positions. However, when installed, it is constrained from being selected to the OFF position by a plastic ridge around the fuel tank selector cover, as shown in Figure 1. This plastic ridge can be stepped on by passengers and damaged. If this happens, the fuel tank selector valve can be accidentally rotated to the OFF position.

Figure 1. Fuel tank selector cover prevents selection of the undocumented OFF position
Figure 1. Fuel tank selector cover prevents selection of the undocumented OFF position

Figure 2. Damaged fuel tank selector cover—fuel selector in undocumented OFF position
Figure 2. Damaged fuel tank selector cover-fuel selector in undocumented OFF position

As seen in Figure 2, the ridge on the plastic cover was damaged, allowing the selector valve to be rotated to the OFF position. The valve was also partially obscured by the water rudder handle, so the pilot relied on feel to determine the switch position, and the incorrect position of the valve was undetected. The fuel in the accumulator tank (approximately ½ gal.) was sufficient to allow the pilot to start the engine, taxi, carry out run-up and before-takeoff checks, and take off, before it was exhausted, shortly after the aircraft became airborne.

There may be a belief that if a fuel selector is in the OFF position, there is insufficient fuel in the lines to start the engine, taxi, carry out run-up and before-takeoff checks, and take off. The accumulator tank in the Cessna 185 contains approximately ½ gal. of fuel. In the event that the valve is OFF and no fuel flows to the accumulator tank, the vapour return line acts as a vent, allowing the fuel in the accumulator tank to be consumed before the engine is starved.

Therefore, keep in mind that in the event of an improper fuel tank selection, there may be sufficient fuel downstream of the selector valve to allow the aircraft to take off before fuel exhaustion occurs. Also, always check the position visually, not by feel.


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