Maintenance error led to gear-up landing

 - May 29, 2008, 10:29 AM

BEECH 1900D, ROCHESTER, N.Y., JUNE 3, 2000–The Safety Board determined probable cause for a gear-up landing by a CommutAir Beech 1900D during a regularly scheduled flight. According to the NTSB, “The reversal of landing gear hydraulic lines by company maintenance personnel [caused the failure]. Factors related to the incident were the manufacturer’s omission of maintenance procedures and the failure of an electrical switch for undetermined reasons.” Neither the pilots nor the 11 passengers aboard were injured in the mishap.

Visual meteorological conditions dominated the route from Washington Dulles Airport (IAD) to the Greater Rochester International Airport (ROC). According to the pilot, the gear retracted normally on departure and nothing unusual occurred en route. When the pilot tried to extend the wheels while on approach to ROC, they failed to come down. The crew executed the abnormal checklist but the gear remained stowed. After two approaches to the field, the pilot departed the area to confer with company maintenance personnel.

According to the NTSB’s final report, the pilots decided to land the airplane with the gear retracted. “The airplane touched down with the belly of the fuselage on Runway 04, a 6,300-ft-long asphalt runway, and skidded to a stop.” When workers lifted the twin turboprop off the runway with a crane, the gear did not free fall.

Safety Board investigators noted: “According to the Raytheon Aircraft Beech 1900D Airliner Maintenance Manual, dated March 28, 1997, a landing gear service valve, which was located in the left inboard wing section of the airplane, was used in conjunction with the hand pump to raise and lower the landing gear for maintenance purposes. Four hydraulic plumbing tube assemblies were connected through ports located on each side of the valve. On the forward-facing side of the valve were the ‘retract port’ and the ‘emergency extend port.’ On the aft-facing side of the valve were the ‘hand-pump pressure port’ and the ‘return port,’ which included a check valve installed between the tube and port. The hydraulic plumbing tube assemblies were also color coded, with the ‘retract port’ receiving a blue marked line, the ‘emergency extend port’ receiving a light green marked line, the ‘hand-pump pressure port’ receiving a yellow marked line and the ‘return port’ receiving an orange marked line.”

A letter written to the manufacturer by the operator said, “We have concluded that the lines to and from the service valve may have been reversed on installation, thereby precluding successful manual extension. The ‘hand-pump pressure tube’ and the ‘pressure tube’ [lines] can be reversed inadvertently.”

Additional guidance for the procedure was added to the maintenance manual by Raytheon on June 15, 2000, reminding the mechanics to “take note” of the direction of flow once they install the service valve. They also told mechanics to “cycle landing gear with the power pack electrically and manually with hand pump before removing the airplane from the jacks.”