Human Performance Factors For Elementary Work and Servicing
Case Study #5: Inappropriate Repair - Gun Tape
Transportation Safety Board Report Number A89O0453
Cessna A185E Skywagon
Jumping Cariboo Lake, Ontario
15 September 1989
Shortly after the aircraft took off from Jumping Cariboo Lake, Ontario, the engine lost power. The pilot commenced a turn in an attempt to return to the lake for a forced landing, but the aircraft descended steeply into a heavily wooded area beside the lake. There was an explosion seconds after impact, and only the pilot was able to escape the aircraft before it was consumed by fire. The two passengers were killed.
The Transportation Safety Board of Canada determined that the engine stopped because of fuel starvation when the fuel selector valve was inadvertently selected to the OFF position, and the aircraft stalled with insufficient altitude to recover.
Other Factual Information
A large portion of the wreckage was consumed by fire. The aircraft systems were consumed to the greatest degree possible, and no evidence of malfunction was found. The pilot reported that the engine was running properly prior to losing power, with no indications of unservicabilities during the run-up, and that the aircraft flight controls were functioning correctly. The aircraft was properly maintained and serviced in accordance with existing regulations, and no preimpact unservicabilities were discovered during a teardown of the engine. Calculations made using witness statements and estimates showed that the aircraft was loaded with the take-off weight below maximum allowable and the centre of gravity within the specified limits. The aircraft's emergency locator transmitter (ELT) was destroyed by fire. The aircraft was not equipped with shoulder harnesses.
The fuel system on this model of aircraft is equipped with a fuel shut-off valve and a separate rotary-type fuel tank selector valve. The selector valve has four positions: OFF, LEFT TANK, RIGHT TANK, and BOTH tanks. The OFF selection is an abnormal position for the selector. The selector valve is normally restricted from the OFF position by a ridge of plastic on a D-shaped plastic fuel tank selector cover. If this cover is damaged at the back, there is nothing to prevent the fuel selector valve from being selected to the OFF position. The location of the fuel selector makes in susceptible to being moved out of the selected position by being kicked inadvertently by a passenger or by shifting cargo.
The pilot stated that the fuel tank selector valve cover had been damaged to the extent that the retaining screws no longer held the cover in place. It was held in place using "high speed" tape. He also stated that the fuel tank selector remained on BOTH virtually at all times. The fuel selector valve from the aircraft was recovered from the wreckage and examined. The valve had been damaged by heat, but it showed no other signs of damage or being otherwise marked. When the selector valve was dismantled, it was found to be in the OFF position. The fuel shut-off valve was not found, thus, it's selected position could not be determined.
The pilot reported that, immediately before the engine lost power, the back of his seat had been kicked by the passenger who was occupying the rear seat, and that both passengers were moving around in their seats.
It is probable that the fuel selector valve was inadvertently moved to the OFF position by a passenger at some point during the take-off or the initial stage of climb. The location of the fuel selector makes it susceptible to inadvertent movement by a passenger's feet or by shifting cargo. It is possible that the passenger in the rear seat kicked the selector, noticed what had happened, and in an effort to correct the change, made the faulty selection to OFF. The engine may have restarted when the fuel pump scavenged enough fuel from the header tank and fuel lines to start the engine momentarily before impact.
A seldom, if ever, used fuel selector was found in a position to which it should not have been capable of being moved. In the BOTH position, a small pointer handle faces forward, and the selector would not be susceptible to a 180 degree movement at the time of impact, particularly without being damaged in the process.
After the engine stopped, the pilot began a relatively steep turn in an attempt to return to the lake for a forced landing. During the turn, the pilot's attention was drawn from flying the aircraft to his efforts to find the reason for the loss of power, and to restart the engine. While he was working on these problems, the airspeed decreased to the point where the aircraft stalled. The pilot attempted to effect recovery from the stall, but had insufficient altitude to complete the manoeuvre, and the aircraft descended into trees.
It was found that:
- The engine lost power shortly after take-off, and the pilot attempted to return to the lake.
- The aircraft stalled at an altitude too low to allow recovery.
- There was an explosion shortly after impact, and an intense fire broke out.
- The aircraft fuel selector valve was found in the OFF position even though it cannot normally be selected OFF.
- It could not be determined what position the fuel shut off valve was in.
The aircraft was not equipped with shoulder harnesses
The engine lost power because of fuel starvation when the fuel selector valve was inadvertently moved to the OFF position, and the aircraft stalled with insufficient altitude to recover.
This report concludes the Transportation Safety Board's investigation into this occurrence. Consequently, the Board has authorized release of this report.
Contributing Human Factors
The main factors contributing to this occurrence were as follows:
- Lack of Communication: Passengers were not given a clear pre-flight safety briefing on accidental manipulation of the fuel selector, or how to avoid such an event.
- Lack of Awareness: Operator was unaware of the possible consequences of not properly repairing the fuel selector.
- Distraction: During the pilot's initial turn back towards the lake, following the engine stopping, his attention was drawn from flying the aircraft to his efforts to find the reason for the loss of power and to restart the engine.
- Norms: If the incorrect repair had existed for an extended period of time, it may have been perceived as an acceptable method.