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ASN Wikibase Occurrence # 58524
Last updated: 17 January 2020
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Time:c. 11:21 LT
Type:McDonnell Douglas MD 900 Explorer
Owner/operator:Aero Asahi
Registration: JA6757
C/n / msn: 900-00018
Fatalities:Fatalities: 0 / Occupants: 2
Other fatalities:0
Aircraft damage: Substantial
Location:Atsugi Airfield, Ayase-City, Kanagawa -   Japan
Phase: En route
Departure airport:Fujiurakona helipad
Destination airport:Tokyo Heliport
Aircraft lost yaw control, followed by No.2 engine failure.
The aircraft tried to make an emergency landing at Atsugi airfield around 11:21, however, ended up a hard landing at west apron of the airfield.
Crewmembers on board were slightly injured.
The aircraft sustained substantial damage.

Due to fracture of a NOTAR Tension-Torsion strap, one blade was detached from the fan hub. The shattered pieces were trapped between rotating and non-rotating parts of fan assembly, causing a temporary seizure of the fan hub. The transmission-side flexible coupling was fractured and anti-flail device kept the driveshaft turning, however, the driveshaft, turning at very high rpm with rotating inertia twisted and fractured at mid-length. This resulted in failure of the fuel supply to the no 2 engine.

According to the information provided by the NTSB, the manufacture’s fatigue load test spectrum
for T-T strap accounted for only the composite load which consists of the centrifugal force load by the NOTAR fan rotation and twist load by manipulation of rudder pedals, and did not account for the case of twist load which may only happen during preflight rudder check or under low NOTAR fan rotation. Those facts are estimated to have contributed to the generation of large compressive/shear strain in T-T straps.


Revision history:

19-Jan-2009 09:56 Peter Added
19-Jan-2009 09:59 harro Updated
19-Jan-2009 21:01 Anon. Updated
26-Sep-2010 14:38 TB Updated [Time, Aircraft type, Registration, Cn, Operator, Total occupants, Location, Country, Phase, Nature, Destination airport, Source, Damage, Narrative, Plane category, ]
26-Sep-2010 15:37 TB Updated [Time]
27-Feb-2013 03:29 TB Updated [Time, Aircraft type, Source]
03-Dec-2013 18:15 Anon. Updated [Date]
22-Aug-2014 14:59 Aerossurance Updated [Departure airport, Damage, Narrative]
24-Dec-2014 16:16 Anon. Updated [Embed code]
24-Dec-2014 16:17 harro Updated [Embed code]

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