Plane & Pilot
Wednesday, March 1, 2006

Overstressing The Airframe

Exercise good preflight and in-flight judgment to keep your airplane intact

Some pilots may believe that an instrument rating and a fair amount of flight time are good insurance against getting into a situation that results in losing aircraft control or exceeding an aircraft’s design stress limits. However, without a healthy amount of good preflight and in-flight judgment, along with recurrent training that includes partial panel work and unusual attitude recovery, those two things can set the stage for getting into trouble. The FAA’s requirements for instrument currency (doing six instrument approaches, holding procedures, and intercepting and tracking courses within the last six months) are less than comprehensive.

The National Transportation Safety Board (NTSB) recently completed its investigation into the in-flight breakups of two Beech Bonanzas. One was a V-tail S35 flown by an instrument-rated pilot with 3,200 hours. The other was a 36TC turbocharged Bonanza with a conventional tail, flown by an instrument-rated pilot who had 1,320 hours. The initial problems encountered were different, but the outcomes were the same.

Beech Bonanza S35
On November 25, 2003, at approximately 6:53 a.m., a Beech S35 was destroyed after it impacted terrain following an in-flight breakup and uncontrolled descent from cruise flight near Warren, Ore. The instrument-rated commercial pilot and his three passengers received fatal injuries. Visual meteorological conditions prevailed at the accident site, but instrument meteorological conditions were reported over the pilot’s route of flight. An IFR flight plan had been filed for the personal cross-country flight being conducted under Part 91. The flight originated from the Arlington Municipal Airport (AWO), Arlington, Wash., at approximately 5:35, and was en route to Rogue Valley International-Medford Airport (MFR), Medford, Ore.

Approximately two hours before the flight, the pilot had received a standard weather briefing from the Seattle Automated Flight Service Station (AFSS). Later, the pilot contacted the AFSS stating that he was on the ground at AWO, had filed an IFR flight plan to MFR, and that he was about 10 minutes late. The specialist told the pilot to hold while he proceeded to coordinate the clearance with the Seattle Air Route Traffic Control Center (ARTCC). At 5:27, the specialist gave the pilot initial clearance to the WATON NDB, climb and maintain 4,000.

At 5:40, radar contact was established with the aircraft at an altitude of 1,400 feet MSL. At 6:35, after having climbed to 11,000 feet, the pilot requested a higher altitude. ARTCC cleared the pilot to 13,000 feet. Radar data indicated that at 6:39, the aircraft had reached 13,000 feet, and the pilot subsequently reported that he was at 13,000 feet and “clear of rime ice.” The pilot radioed to ARTCC, “Ah, we just lost our suction gauge.”

The controller responded, “Climb and maintain 15,000? You requesting a higher altitude? Is that what you said?”

The pilot then replied, “Mayday, mayday, mayday.” There were no further transmissions from the airplane.

Radar data revealed that at 6:50:52, the flight was at 13,100 feet MSL, beginning a right turn from a southerly heading to a south-southwesterly heading and seven seconds later at 6:50:59 was at 12,900 feet MSL, beginning a right turn to a southeasterly heading. At 6:51:04, the aircraft was at 12,800 feet, starting a right turn from the southeast to south-southeast. Seven seconds later, it made a left turn back to a heading of southeast. At 6:51:16, the aircraft had climbed to 12,900 feet and was making a turn farther left to an east-southeasterly heading, reaching 13,100 feet at 6:51:28. Radar data indicated that at 6:51:28, the airplane’s heading changed from east-southeast to a heading of northeast, having descended to an altitude of 10,700 feet by 6:51:52. The airplane then turned back to a heading of east-southeast and descended to an altitude of 10,500 feet at 6:51:59. The aircraft continued on a heading of east until 6:52:05, when its altitude was recorded as being 6,800 feet. It then proceeded on a northwesterly heading until 6:52:17, when the last radar hit recorded the aircraft at an altitude of 6,400 feet.

The fuselage and engine were located approximately 3 nm north-northeast of the Scappoose Industrial Airpark in Scappoose, Ore., and approximately 1 nm northeast of Warren, Ore. It impacted a low-lying marsh area. Both wings, the tail section and the left stabilizer of the airplane were located approximately 1 nm northeast of where the fuselage and engine came to rest.

Records indicated the vacuum pump had been installed 222.5 flight hours before the accident. The vacuum pump was subsequently sent to the NTSB Materials Laboratory in Washington, D.C., for examination. The pump’s rotor and rotor vanes had shattered and the drive coupling shaft was sheared. A second examination of the pump was conducted later, under the supervision of an FAA airworthiness inspector. During that inspection, it appeared as if sometime in the recent past, the pump’s rotor, vanes and coupling were replaced by an unknown party with parts from an unknown source. Although investigators noted that the pilot held an aircraft airframe and powerplant mechanic certificate, the Safety Board did not suggest that the pilot had worked on the vacuum pump.

The NTSB determined that the probable cause of this accident was vacuum pump failure and the pilot’s failure to maintain control of the airplane. Factors contributing to the accident included the instrument meteorological weather conditions and the pilot’s improper recovery from the descent.


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