MU-2B Loses Power, Crashes on Takeoff

 - May 7, 2008, 6:14 AM

Mitsubishi MU-2B-26A, San Antonio, Texas, Jan. 22, 2000–The NTSB’s factual report is now out on the fatal crash of MU-2 N386TM. The twin turboprop was destroyed and both pilots were killed when it crashed immediately after takeoff from the San Antonio International Airport at 1432 CST. The two pilots, one commercial rated and the other a private pilot, were the sole occupants aboard the aircraft, which was owned and operated by BTC Saratoga of Saratoga, Calif. N386TM was on an IFR plan in VMC and had just departed for a cross-country trip to San Jose (Calif.) International Airport (SJC). The commercial pilot had received a standard weather briefing and line-service employees reported that the airplane was topped off before departure.

An employee observed the right engine was started first and allowed to run for about 10 min, and then the left engine was started. According to the ATC transcript, at 1420 while taxiing to the runway, N386TM advised the ground controller that the flight had a “minor delay” and that they would be stopped on the ramp for “a couple of minutes.” The same employee saw someone exit the MU-2, check the nosegear and re-board, after which the airplane taxied to the runway.

At 1430, the crew advised the tower controller that the MU-2 was ready for takeoff and was cleared. A minute later the tower controller advised the crew of N386TM of an MD-80 on a 3.5-mi final and requested that the airplane depart with no delay. N386TM acknowledged and departed, with no further communication from the aircraft’s crew.

Witnesses reported that during the takeoff roll they heard a series of sounds described as a “backfire” or “compressor stall.” Several witnesses reported seeing the airplane’s right propeller “stopped.” One witness reported that as the airplane lifted off the ground, he heard “a loud cracking sound followed by an immediate prop wind down into feather.” He continued to watch the airplane, as the gear was retracted and the airplane entered a climbing right turn. Subsequently, the MU-2 pitched up, entered a “Vmc rollover” and made a 360-deg turn before hitting the ground.

Radar data supported the observations and indicated the airplane climbed on runway heading to a maximum altitude of about 200 ft agl. It then entered a right turn and began to lose altitude. The radar returns revealed that the airplane’s calibrated airspeed was 97 kt when the last radar return was recorded. According to the flight manual, minimum controllable airspeed (Vmc) is 93 kt. At the request of the NTSB, Mitsubishi calculated the airplane’s takeoff weight and center of gravity and found them to be within the normal operating envelope.

Examination of the accident site revealed the airplane hit the ground in a near-vertical attitude. A post-crash fire destroyed all cockpit instruments and switches. Examination of the propellers revealed that neither was in the feathered position at the time of the crash.

Examination of the engines revealed the left engine was operating at the time of impact but the right engine was not, though no anomalies were found that would have precluded normal operation. A fuel sample secured from the fuel truck that fueled the accident airplane revealed that the sample met the specifications for aviation turbine fuel in accordance with ASTM D1655.

The flaps were found to be in the normal takeoff position of 20 deg and the landing gear was retracted. The power lever for the right engine was at the flight-idle position and the corresponding condition lever was in the takeoff/land position. The power lever for the left engine was in the full forward position and its condition lever was also at the takeoff/land position. Additionally, the left and right engine firewall fuel shutoff valves were both found in the open position.

The flight manual’s emergency procedure for an engine failure during the takeoff climb (gear down or in transit to up) is:

1. Landing gear–Down.
2. Operating engine–Power as required.
3. Flaps–Leave in takeoff position.
4. Land straight-ahead using airspeed appropriate for the airplane weight, but not less than 100 kcas.

A warning following this procedure in the flight manual states: “If flaps 20 degrees takeoff is selected and engine failure occurs after liftoff, continued climb performance is not assured unless the landing gear has completely retracted, the gear doors are closed and the flaps are at five degrees or less.”

The left-seat pilot held a private pilot certificate with single- and multi-engine land and instrument ratings. He had logged about 950 hr TT, of which 16.9 hr were in an MU-2 flight simulator and 4.5 hr were in the accident airplane. Although he had started a FlightSafety International MU-2 pilot initial training course, he did not complete the course. His medical was current.

The right-seat pilot held a commercial pilot certificate with single- and multi-engine land and instrument ratings, successfully completed the FlightSafety MU-2 pilot initial course the previous month and had a total of 2,000 flight hours. While at FSI, he flew 20 hr in an MU-2 flight simulator and 16.9 hr in N386TM. His second-class medical was issued June 22, 1999, and stipulated he wear lenses that correct for distant vision and possess glasses that correct for near vision. Toxicological tests for drugs, alcohol and carbon monoxide were negative for both pilots. It has not been determined which pilot was flying the aircraft at the time of the accident.

On Jan. 5 and 6, 2000, a flight instructor flew 4.5 hr with the private pilot and 3.7 hr with the commercial pilot in N386TM to “build time to meet insurance requirements.” Both pilots performed various flight maneuvers, including slow flight, turns (high and low speed) and stalls in all configurations with recoveries.” The instructor pilot “pulled one engine back to idle,” and reported that the commercial pilot “displayed satisfactory performance in recognizing and simulating shutdown and controlling the aircraft.”

On April 15, 1999, among other work done to the aircraft, the right engine underwent a 100-hr inspection. It had accumulated a total of 3,717.7 hr and 3,529 cycles. According to a logbook entry, the right engine was disassembled to “investigate low power.” The diffuser assembly was overhauled and the compressor housing, support assembly, seal assembly and plug seal were replaced. The engine’s Airworthiness Directive and Service Bulletin compliance record was also updated.

Following reassembly of the right engine, the airplane was test flown and found to meet the manufacturer’s specifications. During the test flight, a negative torque sensing (NTS) system check was performed and no discrepancies were noted.

The NTSB determined the probable cause was the pilot’s failure to maintain the minimum controllable airspeed following a loss of engine power during the initial takeoff climb. They listed as contributing factors both pilots’ lack of experience in the aircraft and the loss of right engine power for an undetermined reason.