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Recommendation issued to: Civil Aviation Safety Authority

Recommendation details
Output No: R20040074
Date issued: 25 October 2004
Safety action status:
Background:


On 7 September 2004, at about 0710 Eastern Standard Time, while passing FL175, during a gradual descent from flight level (FL) 220, the pilot of the Raytheon B300 aircraft, registered VH-KJD, heard a loud muffled thud and then air noise. The pilot saw that the cabin door had separated from the aircraft fuselage.

The aircraft was being operated as a single pilot, private IFR flight, from Brisbane to Truganinni, Queensland. A 'safety pilot' occupied the right pilot seat. During the occurrence, the cabin door warning light illuminated and the cabin oxygen masks deployed. The pilots completed emergency checks and actions before diverting the aircraft to Thangool, Queensland.

On 12 September, the cabin door was found in a paddock approximately 3 NM north of Glenbar, Queensland (see Figure 1). The pilot reported that the wind at FL170 was from the south-west at 40 knots.

The investigation found that the aft door latch hook sense switch terminal screw and the sense switch adjustment nut were located in very close proximity (see Figure 2). The manufacturer uses the term 'sense switch' for the electrical switches attached to each of the cabin door locks. These switches provide an indication to the cockpit annunciator panel of the door lock positions.

A circuit test of the three sense switches, located within the door (two switches for the two latch hooks and the other for the door handle position) determined that it was possible for the aft latch hook sense switch to produce an earth point through the sense switch earth loop wiring, resulting in the door handle position sense switch no longer providing an electrical signal for its position. Consequently, one of the systems to alert a pilot to a potential cabin door unsafe condition was not available.

The crew reported that during the flight there had been no warning annunciator panel indication prior to the door opening. The aft latch hook sense switch mounting plate showed no significant distortion and there was no evidence of in-service movement of the aft latch hook sense switch adjustment mechanism.

The investigation is continuing and is examining several aspects in relation to the cabin door separation, including the mechanical locking mechanism of the door.

Output text

Safety Recommendation

The Australian Transport Safety Bureau recommends that the Civil Aviation Safety Authority advise operators of Beechcraft King Air and Raytheon King Air aircraft of the potential safety deficiency of the cabin door warning system becoming prematurely earthed, resulting in a sense switch or switches no longer providing an electrical signal for its or their position.

The recommendation was simultaneously issued as R20040075 to the US Federal Aviation Administration.

ATSB comment:

In response to ATSB Recommendation R20040074 issued on 25 October 2004, CASA issued AWB31-3 issue 1 on 10 February 2005 to address the sense switch problem.

Initial response
Date issued: 07 December 2004
Response from: Civil Aviation Safety Authority
Action status: Closed - Accepted
Response text:

CASA has drafted an Airworthiness Bulletin (AWB) to be sent to all operators of the aircraft highlighting the issue of proximity of the switch and its contact with the airframe.

The AWB is currently awaiting approval and CASA undertakes to inform the ATSB when the AWB is released.

ATSB Comment: On 10 February 2005 CASA issued AWB31-3 issue 1 to address the sense switch problem.

 
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Last update 01 April 2011