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ASN Wikibase Occurrence # 150486
Last updated: 12 November 2020
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Type:Silhouette image of generic P180 model; specific model in this crash may look slightly different
Piaggio P180 Avanti
Owner/operator:Flagship Private Air
Registration: N401WS
C/n / msn: 1057
Fatalities:Fatalities: 0 / Occupants: 2
Other fatalities:0
Aircraft damage: Substantial
Location:Boyne City Municipal Airport, Michigan -   United States of America
Phase: Landing
Departure airport:Detroit, MI (KYIP)
Destination airport:Boyne City, MI (N98)
Investigating agency: NTSB
The pilot stated that, during landing, the nosewheel steering was not engaged and that, after the airplane touched down, it made an uncommanded left turn. The pilot used landing gear braking and reverse thrust to control the airplane, but it still continued to veer left and then off the runway. The airplane struck the airport perimeter fence and a tree and came to rest.

Postaccident examinations and tests of the nosewheel steering system and its associated components revealed that the steering actuator did move uncommanded at varying rates and directions when electrical power was off and hydraulics were engaged to the nosewheel steering system. Further, this occurred as a result of the select/bypass valve's failure to seal properly when in an unpowered state due to incorrect shimming within the select/bypass valve, which allowed hydraulic fluid to enter the servo valve when the system was off. The available hydraulic pressure was then ported to move the steering actuator relative to the position of the servo valve spool. Examinations also confirmed that, when the servo valve was electrically powered off, the spool could slightly free-float, and the unpowered spool position could be biased in the direction of the last commanded travel from when the system was last engaged. Examination of the rest of the airplane revealed no other mechanical malfunctions or failures that would have precluded normal operation.

The nose landing gear assembly was overhauled 7 days before the accident. However, the postaccident examinations revealed that the overhaul was not conducted in accordance with the manufacturer's component maintenance manual and did not meet the requirements of Service Bulletin 80-0249, which was required by Airworthiness Directive (AD ) 2009-21-08 rev 1, even though the maintenance records indicated that the AD was completed and signed off by the operator for the accident airplane.
Probable Cause: The select/bypass valve's failure to seal correctly because of improper shimming, which resulted in an uncommanded and uncontrollable left turn during landing. Contributing to the accident was the overhaul facility's improper overhaul of the steering manifold.




Photo of N401WS courtesy

Oshkosh - Wittman Regional (KOSH / OSH)
25 July 2011; (c) Alex Christie

Revision history:

01-Nov-2012 08:37 bizjets101 Added
01-Nov-2012 08:51 bizjets101 Updated [Source]
08-May-2013 08:23 Anon. Updated [Location]
21-Dec-2016 19:28 ASN Update Bot Updated [Time, Damage, Category, Investigating agency]
28-Nov-2017 13:44 ASN Update Bot Updated [Operator, Departure airport, Destination airport, Source, Narrative]

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