Final Report: Thrust reversers fail on Learjet

 - October 8, 2007, 10:58 AM

BOMBARDIER LEARJET 25C, LEXINGTON, KY., AUG. 30, 2002–The captain’s addition of forward thrust during the landing rollout, resulting in a lack of braking effectiveness, was listed by the NTSB as the cause of a runway overrun accident by Learjet 25C N45CP. A factor was the captain’s inability to deploy the thrust reversers for undetermined reasons.

The airplane, operated as a Part 135 air ambulance by Care Flight International, was fitted with a Dee Howard XR conversion that included thrust reversers. It landed 1,000 feet from the threshold of 7,003-foot Runway 4 at Blue Grass Airport (LEX) in Lexington. About six seconds after touchdown, there was an increase in engine rpm, followed by two expletives from the captain. Slightly less than two seconds later, the captain told the first officer to “brake me,” and after that he said, “Emergency brake.” A few seconds later, there was a “clunk,” followed by a decrease in engine rpm. The captain said, “We’re going off the end.” The airplane dropped off an embankment at the end of the runway, hit a localizer tower and slid across a highway. One passenger–the patient, who was in a seat, not the stretcher–was killed. The captain, first officer, flight nurse and another passenger were seriously injured.

Reverser deployment was hydraulically actuated and electrically controlled. Shortly before landing, the crew confirmed that the hydraulic and emergency air pressures were good, and right and left circuit breakers were in. In addition, the first officer reported “arming one and two.” The captain initially used aerodynamic braking.
Without the use of thrust reversers, the aircraft’s estimated landing distance was about 2,850 feet with the antiskid operative, and 3,400 feet with the antiskid inoperative.

The reverser installation included an accumulator that allowed deploy/stow cycling in the event of hydraulic system failure and interlocks to prevent reverser door deployment until the ARM switch was on, the thrust levers were in idle position and the gear squat switches engaged. The previous crew reported no mechanical anomalies.

Investigation revealed that the thrust reversers were out of the stowed position, but not deployed, and the drag chute was not deployed. However, the brakes were found to operate normally during post-crash testing. Flap position could not be determined due to ruptured hydraulic lines, but the flap position indicator was up. The thrust levers were at idle, and the flap handle was in the down position. The drag-chute handle and the emergency brake handle were in the stowed position; however, the “emergency air” gauge indicated zero.

The captain reported that as the mainwheels touched down, the spoiler switch and thrust-reverser levers were activated. No immediate loss of thrust was felt, confirmed by no “thrust-reverser deployed” lights. The captain “immediately lowered the nosewheel to the runway, and simultaneously stowed the thrust-reverse levers.” Speed was still greater than 100 knots at the time. The captain again tried to activate the thrust reversers, “and no cockpit lights or feel indicated deployment.”

Toe brakes were “lightly” applied, but “gave no indication of slowing the aircraft.” The captain then released and reapplied the brakes with no effect. He then called for the first officer to apply his brakes, but he felt no deceleration. Weather was not a factor, the NTSB said.   &nb