Landing Gear Collapse, Beech Aircraft 200, VH-SGT

FACTUAL INFORMATION¹

Sequence of events

At about 1512 Western Standard Time on 18 January 2005, a Beech
Aircraft Corp B200 (Super King Air) aircraft, registered VH-SGT,
sustained damage when its main landing gear collapsed during
touchdown on runway 24 at Perth Airport, WA.

The aircraft had earlier departed the aerodrome on a charter
flight with one pilot and seven passengers on board. Shortly after
takeoff, the pilot selected the landing gear up and subsequently
observed that the red 'gear-in-transit' warning light remained
illuminated. An aerodrome controller noticed that the aircraft's
landing gear did not retract and passed that information to the
departures controller. The departures controller cleared the pilot
to climb to 4,000 ft and provided radar vectors to a suitable area
where the pilot could complete troubleshooting of the aircraft
systems.

The pilot completed the checklist actions contained in the
Aircraft Flight Manual in an attempt to manually extend the landing
gear. That included pumping the manual extension lever to its
maximum resistance. However, the green 'gear down' indicator lights
did not illuminate² (Figure 1).

Figure 1: Landing gear selector and landing gear
indicator lights

Figure 1: Landing gear selector and landing gear indicator lights

The pilot returned to Perth Airport and conducted a flypast of
the aerodrome control tower and maintenance facility at an altitude
of about 500 ft. Engineer and air traffic control witnesses to that
flypast indicated to the pilot that the landing gear appeared to be
in the extended position.

During the subsequent landing, the right main landing gear
collapsed and retracted into the wheel well. The left main landing
gear partially retracted into the wheel well and the nose gear
remained extended (Figure 2). The right engine nacelle fuel tank
was punctured, requiring removal of the remaining fuel in that tank
prior to the aircraft's removal from the runway.

Figure 2: Aircraft on the runway after
landing

Figure 2: Aircraft on the runway after landing

Abrasive damage was sustained to the rear right side of the
lower aircraft fuselage skin and structure, the right wing flap and
gear doors and rear fairing of the right engine nacelle. The
extended nose landing gear and partially extended left main landing
gear prevented significant damage to other parts of the aircraft's
structure. There was no post-impact fire.

Aircraft information

An approved maintenance organisation carried out end play checks
on the left and right main landing gear screw jack actuators during
routine maintenance on 7 January 2005. Following those checks, each
actuator was disassembled for lubrication, reassembled and refitted
to the aircraft. That required the removal and reinstallation of
each actuator's thrust bearing. The aircraft maintenance manual
included a requirement to recheck the actuators' end play following
their reassembly, to verify the correct installation of the thrust
bearings.

The aircraft was released from maintenance on 11 January 2005,
and completed six flights without incident between 11 and 13
January. On the seventh flight following that maintenance, the
landing gear failed to retract normally. In that instance, the
pilot manually extended the landing gear and landed without
incident. Maintenance troubleshooting following that flight
revealed that the 60 amp circuit breaker for the landing gear's
electric motor had tripped³. The
aircraft's maintenance records indicated that the circuit breaker
was reset and the landing gear was re-rigged and functionally
tested. The system was certified as being serviceable and the
aircraft was returned to service. During the subsequent flight,
flown by the same pilot, the landing gear collapsed.

The aircraft operator examined the aircraft's landing gear
system following the accident. The examination identified that the
landing gear electric motor's 60 amp circuit breaker had again
tripped. In addition, disassembly of the screw jack actuator for
the left main landing gear revealed:

an incorrectly installed thrust bearing⁴
an unseated upper bearing
damage to the inner pinion bearing
displacement of the pinion within its housing
cracks and shearing of the pinion gears.

That damage significantly increased the torque required to
rotate the actuator during either electrical or manual extension of
the landing gear.

A component overhaul facility bench tested another screw jack
actuator with a similarly incorrectly installed thrust bearing
under the supervision of an airworthiness inspector from the Civil
Aviation Safety Authority. That actuator displayed abnormal
squealing and grinding noises during operation, and an increased
amount of torque was required to rotate the screw jack. The test
report indicated that the increased operating loads had unseated
the incorrectly installed thrust bearing, which allowed the
transfer of the load normally carried by the thrust bearing to the
pinion gears, causing binding and abnormal operating noise.

Survival information

Either a pilot in command or the responsible Air Traffic
Services (ATS) personnel can declare a Local Standby condition in
response to a problem, or potential problem affecting the operation
of an aircraft. The effect of such a declaration is to activate an
airport's Rescue and Fire Fighting (RFF) services and other
relevant agencies in accordance with the airport's Aerodrome
Emergency Plan.

In this occurrence, neither the pilot in command nor ATS
personnel declared a Local Standby condition. However, because the
pilot was returning for an unplanned landing, and had requested a
visual check of the landing gear, the aerodrome controller advised
the RFF personnel of the developing situation. The RFF personnel
responded by boarding their vehicles in preparation for a possible
emergency response.

Only those investigation areas
identified by the headings and subheadings were considered to be
relevant to the circumstances of the occurrence.
The illumination of those lights
would have confirmed the successful extension of the landing
gear.
During normal operations, the
landing gear's electric motor provided the torque to rotate the
landing gears' screw jack actuators to extend the aircraft's
landing gear.
It is essential to correctly install
the thrust bearing to ensure that the bearing resists axial loads
along the actuator's shaft. The bearing is appropriately marked to
assist with correct installation.

Maintenance organisation

Following this incident, the maintenance organisation issued a
Technical Memorandum regarding the overhaul of Super King Air
landing gear actuators. That memorandum referred to the requirement
during component assembly, to carefully read and understand the
instructions contained in the aircraft maintenance manual.

The maintenance organisation also submitted a request to the
aircraft manufacturer to include additional warnings in the
maintenance manual to emphasise further the need for the correct
reassembly of the landing gear actuators.

The left main landing gear actuator's thrust bearing was very
likely incorrectly reinstalled during the recent maintenance of
that component. As a result, increased torque was required to
rotate the screw jack actuator in order to retract the landing
gear. That increased torque most probably tripped the landing gear
electric motor's 60 amp circuit breaker during the flight
immediately prior to the accident flight. However, in that
instance, the pilot was able to manually extend the landing
gear.

The torque applied to the screw jack actuator during the
functional test before the accident flight was probably below that
necessary to trip the 60 amp circuit breaker. In addition, that
maintenance action failed to identify the incorrectly installed
thrust bearing, and underlying increased torque required to rotate
the actuator. When the pilot attempted to retract the landing gear
during the accident flight, the increased torque resulting from the
incorrectly installed thrust bearing, together with air loads would
have combined to overload the systems. The result was that the
landing gear electric motor's circuit breaker tripped, and the
pilot was unable to either electrically or manually extend the
landing gear.

The puncture of the aircraft's fuel tank increased the risk of a
post-impact fire, or of another fuel-related hazard during the
landing and subsequent emergency disembarkation. Despite the lack
of a declaration of a Local Standby condition, the action by the
Rescue and Fire Fighting services to board their vehicles
facilitated a rapid emergency response.

At about 1512 Western Standard Time on 18 January 2005, a Beech
Aircraft Corp B200 (Super King Air) aircraft, registered VH-SGT,
sustained damage when its main landing gear collapsed on touch down
on runway 24 at Perth Airport, WA. The aircraft had earlier
departed the aerodrome on a charter flight with one pilot and seven
passengers on board.

The pilot had elected to return to the aerodrome after detecting
a problem during the retraction of the aircraft's landing gear. He
attempted to manually extend the landing gear, but was unable to
confirm that the landing gear had locked in position for the
subsequent precautionary landing. The main landing gear collapsed
as the aircraft touched down.

In the absence of the declaration of a Local Standby condition
by either the pilot in command or the Air Traffic (ATS) services
personnel, the on-airport Rescue and Fire Fighting services (RFF)
were not placed in that condition of readiness for the landing.
However, on receiving advice from ATS of the circumstances of the
aircraft's return for landing, the RFF services personnel boarded
their vehicles in preparation for a possible emergency
response.

Examination of the aircraft landing gear by the aircraft
operator revealed an incorrectly installed thrust bearing in the
hydraulic actuator for the left main landing gear. The result was
that the axial loads normally carried by the thrust bearing were
transferred to the actuator's pinion gears which fractured under
abnormal operational loads. That damage seized the actuator and
prevented the manual extension of the aircraft's landing gear by
the pilot.