Safety Topics
Mayday,
1990-07-01 00:00:00
had failed circumferentially some 13 inches forward of this same attachment. The aft portion of the boom, complete with the empennage, had remained attached to the helicopter by the unbroken, but damaged, tail rotor pitch control rod. It was established that the Tail Boom Failure most forward area of this boom damage was co-incident with the point on the by Mayday tail boom where the tip of a main rotor blade (MRB) would make contact if any were to be deflected sufficiently far down, the shape of this deformation later being matched to that of the MRB cross-section. It was also established contact was stated to be just under two A Hughes 390SH helicopter was to fly that two additional blade strikes had minutes. from its operating base to its maintenance occurred further aft on the tail boom, as base for a 50 hour inspection. The well as two more in the region of the forecast for the flight indicated that the Accident and examination failure on the horizontal stabiliser. At about the time of the final loss of intended route would be affected by fog These four strikes could only have radar contact, several witnesses on the and low stratus. The aircraft flight occurred after structural separation of ground in the area of a small village manual states 'Use engine anti-icing the aft boom. some 4 n milles SSE of Carlisle airport, when OAT is below + 5°C and visible moisture conditions prevail'. Another reported hearing an aircraft which was Strip examination making unusual mechanical noises. aircraft in the area reported that there A strip examination of the rotor Seen emerging from cloud on a southerly was no discernable horizon between the transmission system revealed integrity heading in a position some 600 metres top of the fog layer and the base of the of drive from the engine through to the north of the crash site, it continued to stratocumulus. Visual flight between the main and tail rotors, all damage observed layers was possible but reference to descend while rocking from side to side being caused by the various impacts or with the main rotor slowly turning. At flight instruments was required to subsequent ground fire. The engine and about 150 feet agl, the aircraft was seen prevent disorientation. The ground fuel system strip examination did not momentarily to slow its descent at became visible at 350 feet agl on descent reveal any evidence of pre-impact which point a witness observed some in the accident area. defects, but the presence of unburnt and thing detach from the aircraft and fly in chopped grass throughout the turbine The aircraft took off from Newcastle an arc towards the west. At this point section showed the engine to have been with the stated intention of routing via the main rotor was seen to stop and all cool and rotating only very slowly at the Carlisle to Manchester Barton at 1500 sound ceased and the aircraft then fell time of impact. In addition, there was feet. At 1240 hours the pilot reported vertically to the ground. almost no sign of contact between the overhead Carlisle airport at 2000 feet. rotating and static components within On receipt of an acknowledgement The helicopter had crashed onto a the engine in areas known to rub from Carlisle, the pilot stated that he gently undulating grass covered field following such impacts with an engine was turning south and this was the last aproximately 100 metres from a minor under power. transmission received from the aircraft. road. Examination of the helicopter at The radar derived track indicates that the crash site and later at AAIB Although this type of helicopter is not when the pilot called overhead Carlisle Farnborough, revealed it to have des cleared for flight into cloud or known he was in fact overhead Brampton some cended vertically at a high rate, striking icing conditions it had been equipped 3 n miles to the East of Carlisle. From the ground with a 30° nose down with both an auto re-ignition and an here the aircraft executed a very gentle attitude. It was also laterally level and anti-icing system for the engine. These left turn on to the correct southerly track erect. A post impact fire had consumed systems ae often fitted to engines of this for Barton. A derived speed profile most of the helicopter's structure, type as it is possible for ice to form in the shows that having turned onto south at instruments and flying control linkages engine intake, with the consequent risk Brampton, the aircraft maintained its in the cabin area, but most of the main of engine rundown due to air starvation, cruising speed of 85 knots for about 80 and tail rotors, their transmissions and at temperatures up to + 5°C above seconds before increasing speed. Some the engine were available for examina freezing and in conditions of high 20 seconds later the speed was seen to tion. The helicopter was complete at the humidity. The operating cable of this be rapidly reducing to around 30 knots moment of impact except for the outer system was found complete in the whereupon secondary radar contact half of the horizontal stabiliser. This was wreckage and still connected to the was lost for 33 seconds. On resumption found some 330 metres to the NE of the valve, the frozen relative position of its of radar contact, the aircraft was 400 impact site with a number of small inner and outer sections revealing the metres north-west of the previous fragments from the stabiliser structure valve to have been closed at the time of position and heading south-west at and a main rotor blade end-cap. impact. about 90 knots. Twenty-two seconds Examination of the urburnt tail boom During the wreckage examination, later radar contact was finally lost at revealed an area of severe damage not two defects not related to the accident estimated height of 400 feet agl some consistent with having occurred at were identified. 500 metres south of the crash site. The impact, beginning some 20 inches elapsed time stated from the initial forward of the upper vertical fin leading Reference speed increase to final loss of radar edge attachment. The boom structure AAIB Bulletin 4/90. AIRCRAFT ENGINEERING —Jul y 1990 27
http://www.deepdyve.com/assets/images/DeepDyve-Logo-lg.pngAircraft Engineering and Aerospace TechnologyEmerald Publishinghttp://www.deepdyve.com/lp/emerald-publishing/safety-topics-EFEPIv4G50
had failed circumferentially some 13 inches forward of this same attachment. The aft portion of the boom, complete with the empennage, had remained attached to the helicopter by the unbroken, but damaged, tail rotor pitch control rod. It was established that the Tail Boom Failure most forward area of this boom damage was co-incident with the point on the by Mayday tail boom where the tip of a main rotor blade (MRB) would make contact if any were to be deflected sufficiently far down, the shape of this deformation later being matched to that of the MRB cross-section. It was also established contact was stated to be just under two A Hughes 390SH helicopter was to fly that two additional blade strikes had minutes. from its operating base to its maintenance occurred further aft on the tail boom, as base for a 50 hour inspection. The well as two more in the region of the forecast for the flight indicated that the Accident and examination failure on the horizontal stabiliser. At about the time of the final loss of intended route would be affected by fog These four strikes could only have radar contact, several witnesses on the and low stratus. The aircraft flight occurred after structural separation of ground in the area of a small village manual states 'Use engine anti-icing the aft boom. some 4 n milles SSE of Carlisle airport, when OAT is below + 5°C and visible moisture conditions prevail'. Another reported hearing an aircraft which was Strip examination making unusual mechanical noises. aircraft in the area reported that there A strip examination of the rotor Seen emerging from cloud on a southerly was no discernable horizon between the transmission system revealed integrity heading in a position some 600 metres top of the fog layer and the base of the of drive from the engine through to the north of the crash site, it continued to stratocumulus. Visual flight between the main and tail rotors, all damage observed layers was possible but reference to descend while rocking from side to side being caused by the various impacts or with the main rotor slowly turning. At flight instruments was required to subsequent ground fire. The engine and about 150 feet agl, the aircraft was seen prevent disorientation. The ground fuel system strip examination did not momentarily to slow its descent at became visible at 350 feet agl on descent reveal any evidence of pre-impact which point a witness observed some in the accident area. defects, but the presence of unburnt and thing detach from the aircraft and fly in chopped grass throughout the turbine The aircraft took off from Newcastle an arc towards the west. At this point section showed the engine to have been with the stated intention of routing via the main rotor was seen to stop and all cool and rotating only very slowly at the Carlisle to Manchester Barton at 1500 sound ceased and the aircraft then fell time of impact. In addition, there was feet. At 1240 hours the pilot reported vertically to the ground. almost no sign of contact between the overhead Carlisle airport at 2000 feet. rotating and static components within On receipt of an acknowledgement The helicopter had crashed onto a the engine in areas known to rub from Carlisle, the pilot stated that he gently undulating grass covered field following such impacts with an engine was turning south and this was the last aproximately 100 metres from a minor under power. transmission received from the aircraft. road. Examination of the helicopter at The radar derived track indicates that the crash site and later at AAIB Although this type of helicopter is not when the pilot called overhead Carlisle Farnborough, revealed it to have des cleared for flight into cloud or known he was in fact overhead Brampton some cended vertically at a high rate, striking icing conditions it had been equipped 3 n miles to the East of Carlisle. From the ground with a 30° nose down with both an auto re-ignition and an here the aircraft executed a very gentle attitude. It was also laterally level and anti-icing system for the engine. These left turn on to the correct southerly track erect. A post impact fire had consumed systems ae often fitted to engines of this for Barton. A derived speed profile most of the helicopter's structure, type as it is possible for ice to form in the shows that having turned onto south at instruments and flying control linkages engine intake, with the consequent risk Brampton, the aircraft maintained its in the cabin area, but most of the main of engine rundown due to air starvation, cruising speed of 85 knots for about 80 and tail rotors, their transmissions and at temperatures up to + 5°C above seconds before increasing speed. Some the engine were available for examina freezing and in conditions of high 20 seconds later the speed was seen to tion. The helicopter was complete at the humidity. The operating cable of this be rapidly reducing to around 30 knots moment of impact except for the outer system was found complete in the whereupon secondary radar contact half of the horizontal stabiliser. This was wreckage and still connected to the was lost for 33 seconds. On resumption found some 330 metres to the NE of the valve, the frozen relative position of its of radar contact, the aircraft was 400 impact site with a number of small inner and outer sections revealing the metres north-west of the previous fragments from the stabiliser structure valve to have been closed at the time of position and heading south-west at and a main rotor blade end-cap. impact. about 90 knots. Twenty-two seconds Examination of the urburnt tail boom During the wreckage examination, later radar contact was finally lost at revealed an area of severe damage not two defects not related to the accident estimated height of 400 feet agl some consistent with having occurred at were identified. 500 metres south of the crash site. The impact, beginning some 20 inches elapsed time stated from the initial forward of the upper vertical fin leading Reference speed increase to final loss of radar edge attachment. The boom structure AAIB Bulletin 4/90. AIRCRAFT ENGINEERING —Jul y 1990 27
Journal
Aircraft Engineering and Aerospace Technology
– Emerald Publishing
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