Known And Unknown Deficiencies

Occasionally, NTSB accident investigators find that a pilot wasn't terribly smart when taking off, knowing that there was something wrong with the aircraft. The Safety Board often describes this in Probable Cause statements by saying that the pilot "attempted flight with known deficiencies in equipment." Unfortunately, whether the deficiency was known or unknown, the outcome can be the same.

Piper PA-28RT-201
On July 2, 2002, at 3 p.m., a Piper PA-28RT-201 operated by a flight school struck the ground during initial climb after takeoff from Lebanon Municipal Airport in Lebanon, Tenn. The Part-91 instructional flight was being operated VFR and the aircraft had been flown to Lebanon from Nashville, Tenn. The flight instructor and the private pilot who was receiving instruction sustained fatal injuries, and the commercial-rated passenger who was sitting in the back received minor injuries.

During the engine run-up, the passenger noticed that the checklist was not used. However, a magneto check was performed. It indicated that the left magneto operated normally, but when the right magneto was selected, the engine lost power. The pilot and the CFI made the decision to continue the flight on one magneto, since it had been done successfully in the same plane during the previous week.

The flight took off from runway 19. When the airplane was passing over trees, the passenger heard the CFI tell the private pilot to "watch the airspeed, and keep it straight." The passenger looked out of the window and noticed that the airplane was slightly nose-up and felt the "airplane sinking." The CFI took over the flight controls and banked the airplane to the right. The passenger remembers seeing a barn from the air and the airplane hitting a power line.

Witnesses at the airport observed the flight during the departure and reported that the airplane sounded normal, but it didn't appear to climb normally, as if it was unable to gain altitude. One witness reported that as he watched the airplane pass, he could see the top of the wings because the nose was high. Another witness, a private pilot, stated that the airplane started to climb with the tail very low, and "it never climbed much." Witnesses watched the airplane travel down the runway and fly low over the trees. They saw the right wing drop dramatically, and the airplane disappeared behind the trees.

The certified flight instructor held a commercial-pilot certificate with airplane single-engine and multi-engine land, and instrument ratings. His total flight time was approximately 1,675 hours. His approximate flight time in the Piper Arrow was not determined.

The private pilot was rated for airplane single-engine land and instruments. Total flight time was approximately 145 hours, with time in type not determined.

A review of the aircraft's maintenance records did not disclose any previous work written up as having been performed on the magnetos or engine ignition system. The left and right magnetos were removed for further examination. The magnetos exhibited signs of previous maintenance and the tamper-proof torque seal had been disturbed on both. The left magneto was put on a test bench and run at 100-rpm increments from zero to 2,700 rpm. The magneto functioned normally throughout the operating range. The right magneto was put on a test bench and also run at 100-rpm increments from zero to 2,700 rpm. Erratic spark conditions were noted on the spark leads that are up to 1,500 rpm. From 1,600 to 2,600 rpm, the spark was consistent, and at 2,700 rpm, the magneto sparked normally. According to the passenger, he performed the first flight from Nashville to Lebanon, where he conducted two touch-and-go landings.

Investigators noted that an FAA Advisory Circular states that dual magneto systems are designed to provide redundancy so that, in case one magneto fails, the pilot will be able to proceed to the nearest suitable airport and land under power. It explains that, although an engine can run on only one magneto, only one set of spark plugs will be firing and the quality of combustion and power output will be affected. Investigators also noted that the operating handbook for the airplane called for running the engine with "both" magnetos selected.

The NTSB determined that the probable cause of this accident was the certificated flight instructor attempting flight with known deficiencies in equipment, the inoperative magneto and the subsequent loss of engine power, and collision with a transmission line while maneuvering for a forced landing.

Mitsubishi MU-2B-35
On August 1, 2001, about 7:51 a.m., a Mitsubishi MU-2B-35 crashed in Hilton Head, S.C. The airplane was a twin-engine turboprop. Visual meteorological conditions prevailed and an IFR flight plan had been filed. The sole occupant of the aircraft, a commercial-rated pilot, received fatal injuries and the aircraft was destroyed in the post-crash fire. The flight originated from Savannah, Ga., about 10 minutes before the accident. The flight was going to Hilton Head to pick up cargo.

According to the controller who was handling the flight, at 7:50, he noticed on radar that the airplane had initiated a gradual descent from 2,000 feet to 1,000 feet. At 7:51, the altitude rose slightly to 1,300 feet and then the target disappeared from the radar screen.

According to a person at the Hilton Head Airport who was monitoring the Unicom frequency, the pilot asked for traffic advisory while approaching the airport. He advised the pilot that traffic was landing and departing from runway 3. The pilot responded, saying, "Thank you. Traffic landing and departing runway 3." That was the only communication with the pilot via Unicom.

Witnesses reported seeing the aircraft in a right, wing-down, nose-low flight attitude as it initially impacted trees and crashed on a golf course.

The pilot held a commercial certificate, with airplane single-engine and multi-engine land, and instrument-airplane ratings. He also held a commercial-helicopter certificate with an instrument rotorcraft rating, as well as an FAA Airframe and Powerplant mechanic certificate. At the time of the accident, he had accumulated about 4,100 flight hours, with about 500 flight hours in MU-2 airplanes.

The airplane was being maintained under an FAA-approved aircraft inspection program. About 87 flight hours before the accident, the airplane was inspected per Airworthiness Directive (AD) 88-23-01, which required the disassembly, inspection and reassembly of the flap torque tube joints.

During the examination of the wreckage, investigators found that the flap torque tube assembly between the flap motor and the flap stop assembly had disconnected. The flap torque tube assembly's female coupler, which attaches to the male spline end of the flap motor and flap stop assembly, was found with a cotter pin installed through the female coupler of the flap stop assembly. The cotter pin had not been placed through the spline and the coupler, consistent with normal installation, as per Mitsubishi's maintenance manual and as specified in Service Bulletin 189. The cotter pin missed the male spline on the flap motor. In addition, the flap coupler on the opposite side of the flap motor did not have a cotter pin installed.

Measurements taken during the wreckage examination revealed that the flap on the left side was fully extended to the 40-degree position, while the flap on the right side had been extended to only 20 degrees.

The NTSB determined that the probable cause of the accident was improper maintenance/installation and inadequate inspection of the airplane's flap torque tube joints during routine maintenance by company maintenance personnel, which resulted in the right flap torque tube assembly coupler becoming detached and the flaps developing asymmetrical lift when extended, which resulted in an uncontrolled roll, a descent and an impact with a tree during the approach to land.

Peter Katz is editor and publisher of NTSB Reporter, an independent monthly update on aircraft accident investigations and other news concerning the National Transportation Safety Board. To subscribe, write to: NTSB Reporter, Subscription Dept., P.O. Box 831, White Plains, NY 10602-0831.