Under The Cowling

Beech A45
A Beech A45 crashed during a forced landing near Boulder City, Nev. The commercial pilot and his passenger were killed, and the airplane sustained substantial damage. The day/VFR flight had taken off from Chandler, Ariz., and was headed for North Las Vegas Airport (VGT), Las Vegas, Nev.

While cruising at 9,500 feet MSL, the pilot radioed Las Vegas Terminal Radar Approach Control (LAS TRACON) to request priority handling because an engine chip light had illuminated. Then, the pilot radioed that he had lost a cylinder, and declared an emergency. He said that he'd try to land at Boulder City Municipal Airport (BVU). The controller approved a switch to the BVU common traffic advisory frequency (CTAF).

Prior to switching frequencies, the pilot reported that the airplane was at 3,800 feet with the landing gear down, and the situation was under control. There was no other contact from the pilot with TRACON or on the CTAF. The airplane crashed about one mile west of the Boulder airport.

Investigators determined that the airplane's original logbooks were lost; the current logbook was started on July 3, 1993, at a total time of 5,335.4 hours and a tachometer time of 581.4 hours. The tachometer read 691.5 at the last annual inspection on March 1, 2012.

The Continental IO-550-B23B engine was a factory-remanufactured zero-time engine installed on June 21, 1996.

The pilot was an FAA-authorized mechanic, and was performing maintenance on the airplane himself. An annual inspection was in progress, and work completed included replacement of all six cylinders with new cylinders. He had flown the airplane to Chandler for a required inspection of the wings the day before the accident.

Investigators found written evidence the pilot/mechanic had advised the airplane's owner that, three days prior to the accident, the engine had been operated. The pilot/mechanic advised that it ran well, and the airplane was nearly ready for flight.

Investigators also were given access to an email to the owner sent the evening before the accident, which stated that the inspection in Chandler had been difficult, because the pilot/mechanic had spent a lot of time looking for tools and parts. The email reported the pilot/mechanic planned to return the airplane to North Las Vegas the following day. It noted that the airplane was flying great, and the cylinder head temperatures were coming down and equalizing. The pilot/mechanic said that the day after going back to North Las Vegas, he'd complete all paperwork and billing for the work performed and return the airplane to service.

The weather at Boulder at the time of the diversion included wind from 140 degrees at 25 knots gusting to 30 knots and visibility 10 miles with clear skies.

Investigators who examined the wreckage noticed that the nose landing gear separated and was in the first part of the debris field. Both main landing gears remained attached and were extended. Both flaps were in an extended position. This indicated that the airplane was configured for landing.

Numerous metal chunks were in the engine oil sump. Metal flakes contaminated the oil filter element, and metallic debris was on the chip detector.

The airplane was equipped with a warning light annunciator panel that included two chip lights. The panel was sent to the NTSB Office of Research and Engineering for examination. The filaments in both chip light bulbs exhibited stretching, indicating they were illuminated at impact.

The NTSB Materials Laboratory examined the number-six cylinder and other engine components. As part of the engine design, the number-six cylinder was attached to the crankcase by six case studs and two through bolts that passed through the base flange of the cylinder. The cylinder was designed to be further clamped to the case by a deck plate on a seventh stud located between the number-six and number-four cylinders. The two through bolts passed through the forward flange of the number-six cylinder. The nuts were missing. Threads of both bolt ends showed radially oriented contact damage, but no overall outward shearing or deformation of the thread forms.

The aft upper stud had been pulled from the case and retained in the flange of the cylinder; its nut remained fully threaded onto the stud. Approximately four or five case threads were stripped from the crankcase with the thread remnants retained in the stud threads. The cylinder fins directly outboard of this stud were deformed, consistent with contact with the end of the stud.

The examination revealed that the seventh stud had its nut present, but not the deck plate that in normal assembly was under the nut and in contact with the adjacent cylinder flange. The metallurgical exam noted that the stud appeared intact with the stud threads showing some contact deformation on the number-six cylinder side. The contact area was in an area that in normal assembly was concealed by the deck plate.

Visual examinations of the mounting pad for cylinder number six revealed areas of fretting damage adjacent to both through bolts, at the two forward studs and the two remaining upper studs. The pad surface at the lower two rear studs had a raised lip of material corresponding to the edge of the cylinder, and this was consistent with the cylinder rocking toward those studs.

The NTSB determined that the probable cause of this accident was the pilot/mechanic's loss of control during an emergency descent following a loss of engine power while in cruise flight. Contributing to the accident was the pilot/mechanic's incorrect assembly of the No. 6 cylinder at the last cylinder change, which resulted in a separation of the cylinder and the loss of engine power.

Aerostar 601P
The NTSB also recently completed its investigation into the crash of a Smith Aerostar 601P one-half mile north of the Austin-Bergstrom International Airport (AUS), Austin, Texas. The pilot, who was the only person on board, was killed. The airplane was destroyed. The flight originated from the Dallas Executive Airport.

The pilot had been receiving VFR services from AUS Approach Control, and was being vectored toward runway 17L. Although the approach controller handed off the pilot to the tower, the pilot never contacted the tower controller. The tower controller could see smoke north of the airport. The wreckage was located by units from the Austin Fire Department.

Witnesses reported seeing a slow-flying airplane at low altitude. The left engine was at a low rpm and "sputtering, knocking" or making "banging" sounds, and trailing black smoke.

The airplane was powered by two Lycoming IO-540-S1A5MM engines, each rated at 350 hp.

According to a previous owner, during the 2011 economic downturn, the airplane was taken out of service and sat dormant on an open ramp at Patterson, La., for over two years. The accident pilot purchased the airplane, refurbished it and filed for a new registration.

Examination of the left engine revealed the rubber boot that connected the intercooler to the fuel injector servo had become dislodged and had been partially sucked in toward the servo. The clamp used to secure the hose was loose, but remained around the servo. The safety wire on the clamp was in place, and the clamp wasn't damaged. The exhaust tubing also exhibited dark sooting, likely a result of the engine operating with an excessively rich mixture.

The NTSB determined that the probable cause of this accident was the pilot's failure to maintain sufficient clearance from trees during the single-engine landing approach. Contributing to the accident was the loss of power in the left engine due to an improperly installed rubber boot that became dislodged and was then partially sucked into the fuel injector servo, which caused an excessively rich fuel-air mixture that wouldn't support combustion.

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, visit www.ntsbreporter.us or write to: NTSB Reporter, Subscription Dept., P.O. Box 831, White Plains, N.Y. 10602-0831.