Fuel starvation caused Bembridge plane to crash

first picture of aircraft crash at bembridge

The Air Accident Investigation Branch (AAIB) has today (Thursday) published a report into last July’s plane crash in Bembridge, which seriously injured 2 people.

On the afternoon of 12th July 2018, a Beagle B121 Series 2 Pup – registration G-TSKY – was forced to make an emergency landing in marshland between Bembridge and Brading shortly after taking off from Bembridge Airport.

Given the remote area of the incident, the report states that it understandably took the emergency services just over 30 minutes to find the scene after they received the first report, which was made approximately 20 minutes after the accident. It took a further 23 minutes after the first emergency services reached the site before specialist medical assistance could be provided to the pilot and passenger, who suffered a mix of head and back injuries.

Now, almost a year after the incident, investigators have drawn a conclusion to the cause of the crash. The AAIB say that the most likely cause was a loss of power due to fuel starvation, although the cause of the fuel starvation has not been determined.

The crash
The aircraft took off from Kemble Airfield at 12.24pm on 12th July before landing at Bembridge around 1.30pm. The pilot and his passenger stopped off for some refreshments and then prepared to take off again at 2.15pm.

The official air accident report says that when the pilot started the aircraft engine for departure, he heard a noise that he had not heard before. After consulting with another member of a flying group and having satisfied there was nothing obviously wrong, with all pre-flight checks appearing normal, the pilot proceeded to take off.

At 2.27pm the aircraft was seen to begin its takeoff from Bembridge. The pilot has recalled to investigators that the takeoff was normal and that as the aircraft passed 300 ft aal in
the climb he retracted the flaps as required in the checklist. Shortly afterwards he sensed that the engine power was decreasing rapidly. There was no noise or change of note that he detected. He concentrated on flying the aircraft, lowering the nose and looking out for a suitable landing area. The area ahead did not look particularly flat for a forced landing, but he assessed that he was at too low a height to attempt to manoeuvre the aircraft.

He completed some of the forced landing checks but very quickly the aircraft was approaching the ground. There was a loud thump as the aircraft struck the ground. The pilot suffered a head injury which rendered him unconscious for some time, as well as other injuries including to his back and pelvis.

The passenger described the takeoff as “fine” until the aircraft passed the upwind end of the runway. She described the engine “switching off” with no noises or vibrations. The aircraft then began a descent with the pilot “moving some switches”. As the aircraft struck the ground, she suffered injuries to her back. As she could smell fuel, she was fearful of a fire and managed to undo her harness before extracting herself from the cockpit. Due to the pain in her back she was unable to move beyond the wing.

The response
The pilot had made a MAYDAY call after the loss of power on Bembridge Airfield’s Air/Ground radio frequency, which was unmanned at the time of the accident. This radio call was heard by the pilot of another aircraft, who contacted Sandown Airfield by radio to report it. Further information was then received on Sandown’s frequency from an aircraft who had noticed the aircraft wreckage.

At 2.50pm, the police were alerted at Sandown Airfield by someone flagging down a patrol car. A helicopter pilot on Sandown’s frequency, who was inbound, passed close by where the accident was reported to have occurred and offered to search. He saw that the aircraft was in marshland beyond the airfield almost aligned with the runway. He was able to land some distance from the wreckage, and he and his two passengers made their way to the aircraft to see if they could offer assistance.

The accident site was difficult to access, located in marshland 580 m from the end of Runway 30 at Bembridge and 105 m right of its centreline.

Sometime after 2.50 the helicopter pilot at the accident site told the police emergency call handler that the accident site was not on the airfield. He stated that he could clearly hear the sirens but that they were on the airfield rather than near where the aircraft was located. He attempted to direct the emergency services to the site, but they could not find a route to access the marshland.

At 3.23pm the emergency services began to arrive at the site, firstly on foot and then using specialist all-terrain vehicles. The pilot and passenger were evacuated by the Hampshire and Isle of Wight Air Ambulance and the Thames Valley Air Ambulance.

The findings
Specialist investigators state that no engine defects or mechanical failures were found that would explain a loss of power. The magnetos and spark plugs worked correctly when tested. The atmospheric conditions were not conducive to carburettor icing and the air intake was clear of blockages. Therefore, the most likely cause of the loss of power was fuel starvation.

Based on recent fuel uplifts and fuel burn calculations there should have been sufficient fuel onboard, and the findings of fuel in the soil beneath the wreckage support this conclusion. Therefore, some fuel system‑related issue probably prevented sufficient fuel from reaching the engine. A blocked fuel tank vent in the left landing gear leg could have prevented fuel flow. Although the vent was found to be clear it is possible that some debris fell out in the impact.

The location of the fuel tank vent, low on the left landing gear leg, could make it prone to picking up debris from a runway, and as both tanks are vented from this single point, a single blockage could result in a loss of power. The pilot reported having removed the fuel tank filler caps prior to departure from Bembridge which would have vented the tanks to atmosphere. If the vent had been blocked it is unlikely that in the short time from engine start to power loss, a sufficient vacuum would have built up in the tanks to prevent fuel flow.

A nut at the carburettor inlet that was loose and not wire locked could have resulted in a leak sufficient to cause a loss of power but not in the position as found. However, it is possible that the nut was tightened in the impact by forces acting at the union when the carburettor separated. It is also possible that some debris entered the carburettor and caused a fuel flow restriction, but that this debris was released when the carburettor broke open on impact.

The AAIB say that the nuts between the engine-driven fuel pump and the carburettor should have been wire locked in accordance with the aircraft maintenance manual.

No explanation was found for the “strange” noise heard by the pilot and passenger after the first engine start