HILLSBORO, OR, USA
N6017P
Piper PA-24-180
The flight instructor reported noting a discharge indication on the aircraft's ammeter during flight. Despite being unable to restore a positive charge indication, the crew (a pilot undergoing a flight review and her flight instructor) elected to continue the flight. The aircraft lost electrical power on approach to the airport, and the aircraft's landing gear collapsed on landing. Although the crew reported they observed a gear-down indication prior to the loss of electrical power, a witness who observed the aircraft from a vantage point near the approach end of the runway reported that the aircraft's landing gear was not fully extended on final. The aircraft has electrically actuated retractable landing gear. A post-accident examination of the aircraft's electrical system disclosed a normally functioning alternator, an aircraft bus voltage of 11.35 volts when energized with the aircraft battery (nominally 12 volts), and a loose alternator drive belt.
On May 23, 1999, approximately 1634 Pacific daylight time, a Piper PA-24-180 airplane, N6017P, sustained substantial damage in a landing with less than full gear extension on runway 2 at Portland-Hillsboro Airport, Hillsboro, Oregon. There were no injuries to the airplane's three occupants, consisting of the commercial pilot-in-command, a flight instructor, and a rear-seat passenger (who owned the airplane.) Visual meteorological conditions prevailed and no flight plan was filed for the local 14 CFR 91 instructional flight, which originated at Portland-Hillsboro. The flight was conducted to accomplish a flight review and instrument proficiency check for the pilot-in-command. Information furnished by the FAA during initial accident notification indicated that the airplane performed a 270-degree turn for traffic prior to its approach, and that the airplane executed a go-around after tower controllers informed the pilot that the airplane's landing gear did not appear to be down. On the next approach, the tower again informed the pilot that the airplane's landing gear did not appear to be down, but the airplane continued to land. The airplane either landed gear-up (or with partial gear extension) or experienced a gear collapse during landing. In an initial interview with an FAA inspector, the flight crew reported that they observed a "down-and-locked" landing gear indication prior to the occurrence. A nose landing gear arm was noted to be broken during post-accident examination; however, the FAA inspector who examined the aircraft after the accident reported to the NTSB that he found no evidence of pre-existing malfunctions or damage in the airplane's landing gear system. The broken component was removed from the accident aircraft and sent to the NTSB's Northwest Regional Office, Seattle, Washington. In a visual examination of the component fracture surfaces, the NTSB investigator-in-charge (IIC) observed no evidence of a pre-existing fracture. In a written statement submitted with the pilot's NTSB accident report, the flight instructor subsequently stated that the instrument proficiency check portion of the flight was terminated after the automatic direction finder (ADF) needle twice failed to indicate station passage, necessitating a recycle of ADF system power each time in order to regain normal ADF function. The flight instructor further reported that he subsequently "noticed a slight discharge indication on the ammeter." He stated: We proceeded to shut down every piece of equipment aboard, one at a time, monitoring the ammeter. At best the ammeter's needle moved from just slightly off center (toward discharge) to neutral. As we reversed this procedure, we noticed no single device that affected the indication, all of which returned the needle to slightly off center (discharge). The flight instructor indicated that after noting the ammeter discharge, the flight was continued, noting that "We experienced no communication problems with [Portland] approach...." Both pilots reported in their written statements that upon returning to Hillsboro and maneuvering for traffic sequencing, the landing gear was lowered, and the green gear position indicator light checked (all of the aircraft occupants reported that it was on.) The flight instructor reported that while established on short final, he and the pilot "looked at each other and noted that we had lost electrical power (intercom, radios and the gear indication green light)"; the pilot reported that as the airplane neared Cornell Road (approximately 1/4 mile final for runway 2), she realized "we were unable to contact the tower" and that "we couldn't talk to each other either." Both pilots reported that as a result, they elected to make a full-stop landing. The pilots reported that the landing initially seemed normal until roll-out was commenced, at which point the flight instructor "began to sense a slow sinking perception." The flight instructor reported that at this point, he "immediately grabbed the control wheel and pulled it full aft", which ultimately did not prevent the nose from lowering and contacting the runway. The aircraft came to a stop on the runway. A witness who reported he observed the aircraft from the Hillsboro airport's west parking lot (at the end of runway 2) stated to an FAA inspector in a telephone interview on the day after the accident that "he observed an aircraft just outside of [the] threshold, looked at [its] gear which caught his attention [and] could not tell if it was fully extended, but [it] was extended." The witness, who reported to the FAA inspector that he was a private pilot, reported that "As the aircraft came a beam [sic] of his position...he could tell that the landing gear was not fully extended." On August 4, 1999, an inspection of the electrical system of the accident aircraft was conducted at Double G Aviation of Hillsboro, Oregon, with inspectors from the FAA's Hillsboro, Oregon, Flight Standards District Office (FSDO) present. The FAA inspectors reported the findings of this examination as follows: a. The alternator drive belt was very loose. When pressure was applied to nut securing the pulley to the front of the alternator, slippage occurred at 8-inch pounds [sic]. The Piper Comanche Service Manual...specifies 7 to 9-foot pounds [sic] for a 3/8 inch used belt.... b. The loss of belt tension was a result of wear at the bolt hole in the alternator housing. The mounting bolt passes through a boss at the base of the housing and secures the alternator to the mounting bracket. This boss is approximately 1-inch long and provides all the support for the alternator. Noticeable movement took place when forward and aft pressure was applied to the housing.... c. The alternator was checked for operation and was capable of supplying power. Double G Aviation, in its report on the examination, further noted that total deflection of the alternator belt as found exceeded 1.5 inches, and that the aircraft bus voltage was measured at 11.35 volts when energized by the aircraft battery (nominal battery voltage is 12 volts.) Double G Aviation's report concluded: Due to the looseness of the alternator belt exhibited, [it] is our opinion that the alternator would not have been able to support the aircraft's electrical requirements. It is also our opinion that the alternator system, with proper belt tension and repair of the damaged mount, would operate normally.... The PA-24-180 utilizes electrically actuated landing gear. On her NTSB accident report, the pilot indicated that the aircraft total time was 4,249 hours, its last annual inspection was performed on August 14, 1998, and that the aircraft had been flown 36 hours since the last inspection.
A loose alternator drive belt, and the flight crew's decision to continue flight with a known electrical system deficiency, resulting in disabling of the aircraft electrical system and landing with the gear not down-and-locked.
Source: NTSB Aviation Accident Database
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