One horizon too far
PUBLISHED: 10:38 23 June 2011 | UPDATED: 14:03 10 October 2012
The pilot planned to fly his Gardan Horizon from Bagby to Panshanger and return. Refuelling prior to takeoff, he calculated that it was a three-hour flight for which he required about 120 litres, which equated to the main tanks being three-quarters full. The fuel
The pilot planned to fly his Gardan Horizon from Bagby to Panshanger and return.
Refuelling prior to takeoff, he calculated that it was a three-hour flight for which he required about 120 litres, which equated to the main tanks being three-quarters full. The fuel gauges indicated that the main tanks were about one-quarter full, so he added 85 litres. The aircraft also had an auxiliary fuel tank containing about 15 litres, which the pilot considered as his emergency reserve. He decided not to take full fuel as he wanted to make an allowance for baggage and had also considered the performance consequences of wet field conditions after recent heavy rain.
With pilot, three passengers and fuel, the aircraft was within its certified weight and centre of gravity limitations. During the return flight to Bagby the pilot noticed the main fuel gauge readings were lower than expected, which he attributed to “the notorious fuel gauge inaccuracies”, and, since the flight time was as planned, he was not unduly concerned. However, when the aircraft was some six miles from Bagby the engine faltered, then stopped.
The pilot selected a field for a forced landing and trimmed to glide speed. As he approached his chosen field he selected landing gear down, an action that, on the Horizon, automatically lowers the flaps. The pilot had not anticipated the effect that extended landing gear and flaps would have on the aircraft’s glide angle and it descended into a hedge short of the intended field, turning over and coming to rest inverted.
None of the occupants were injured. The pilot considered that the accident was caused by him not putting enough fuel into the main tanks when he refuelled.
He noted that he still had fuel in the auxiliary fuel tank and, had he remained calm, he could have selected that tank. In its report the AAIB comments that fuel consumption curves shown in the Horizon’s Operating Manual contained an error, where the data for fuel consumption in litres per hour was incorrectly aligned with the graph so that, for example, 10US gallons is incorrectly aligned with 30 litres, whereas it should be aligned with 37.8 litres. The net effect in this case was that the pilot had calculated his consumption, including a 20% margin, to be approximately 38 litres per hour, whereas it should have been some 46 litres per hour.
“Although he was not helped by the incorrect conversion data that were published in the Operating Manual…had (the pilot) selected the auxiliary tank when the engine started to falter, it is likely that the accident could have been averted,” says the AAIB. As a result of this accident the European Aviation Safety Agency subsequently issued an Airworthiness Directive that forbids the use of the existing conversion curves and provides correct conversion data that is to be inserted into the Horizon’s Operating Manual.