Safety Issue
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.
