NEWPORT, NH, USA
N44438
Piper PA-28-151
After departing and climbing to a cruise altitude of 6,500 feet above mean sea level, the pilot made a power reduction to descend below a cloud layer. After reducing power the throttle became stuck. Unable to move the throttle, the pilot diverted to an alternate airport. With the engine still running the airplane touchdown on the runway, but the pilot was unable to stop the airplane. The airplane exited the departure end of the runway, traveled 75 feet, and came to rest on top of a hill. While landing, the pilot thought the throttle was in the idle position. After the accident he realized it was slightly open. Examination of the carburetor, which had 12 hours since overhaul, revealed that the throttle shaft could not be rotated by hand, and a punch and hammer was required to remove the shaft. The shaft was galled where it rested on the bushings. Both ends of the original shaft (part number CF 13-1521) measured .3105 of an inch in diameter. A new shaft supplied by the overhaul facility measured .3104 of an inch in diameter at both ends. Under the supervision of the NTSB Investigator, the original throttle bushings were re reamed with the original router. Then, the new throttle shaft was inserted, and it rotated freely. The old shaft was then inserted, but was difficult to rotate. After removing the old throttle shaft, the bushings were re reamed, using a new router the company had bought after the accident. Again, the old shaft was inserted, but this time it rotated freely. The butterfly valve was then installed, and the throttle shaft continued to rotate without difficulty
On July 24, 1998, at 1158 eastern daylight time, a Piper PA-28-151, N44438, owned and operated by the East Coast Aero Club Inc., was substantially damaged when it ran off the end of the runway at Parlin Field Airport, Newport, New Hampshire. The certificated private pilot and three passengers received minor injuries. Visual meteorological conditions prevailed for the personal flight that originated at the Laurence G. Hanscom Field Airport, Bedford, Massachusetts, about 1100, destined for Burlington International Airport, Burlington, Vermont. A visual flight rules flight plan had been filed for the flight conducted under 14 CFR Part 91. According to the pilot, after he departed Bedford and was established in cruise flight at 6,500 feet above mean sea level, he made a power reduction to descend below a cloud layer. When he reduced the throttle he felt it stick, in what he though was the idle position. He then verified that the friction was off and that he could move the mixture lever. According to the pilot the throttle and mixture share a common control. The pilot added that he unsuccessfully attempted to move the throttle using two hands, in both directions. At that point, he decided to divert to Newport, New Hampshire, and advised Boston Center who was providing him with radar traffic advisories. The pilot stated that he circled once over the Newport Airport to lose altitude then entered the traffic pattern for Runway 18. On final, according to the pilot, he was fast, and high. He added that he "landed long," and was unable to stop the airplane before it reached the end of the runway. The airplane came to rest approximately 75 feet past the departure end of Runway 18 on top of a small brush covered hill. All four occupants sustained minor injuries, and were able to egress under their own power. The pilot stated that earlier in the flight he could move the throttle freely, except when it was close to the full open or idle position. He added that after the accident he realized the throttle was in fact stuck slightly open. On November 19, 1998, at the NTSB Northeast Regional Office, the carburetor which had a total of 12 hours since overhaul was examined under the supervision of the NTSB Investigator. Also present for the examination, were two representatives from the maintenance facility that overhauled the carburetor last. Prior to disassembling the carburetor, the throttle shaft could not be rotated by hand, and under the investigator's supervision a maintenance person provided by the overhaul facility had to use a punch and hammer to remove the throttle shaft. Examination of the carburetor throttle shaft revealed galling on the throttle assembly side of the shaft where it rested on the bushing. Galling was also observed on the shaft, opposite of the throttle assembly, where the shaft contacted the bushing. Both ends of the original shaft (part number CF 13-1521) measured .3105 of an inch in diameter. A new shaft supplied by the overhaul facility measured .3104 of an inch in diameter at both ends. Under the supervision of the NTSB Investigator, the original throttle bushings were re reamed with the original router. Then, the new throttle shaft was inserted, and it rotated freely. The old shaft was then inserted, but was difficult to rotate. After removing the old throttle shaft, the bushings were re reamed, using a new router the company had bought after the accident. Again, the old shaft was inserted, but this time it rotated freely. The butterfly valve was then installed, and the throttle shaft continued to rotate without difficulty.
The seizure of the throttle shaft, due to the overhaul facilities' failure to insure all metal fragments had been removed from the carburetor before inserting the throttle shaft after reaming the throttle shaft bushings.
Source: NTSB Aviation Accident Database
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