NTSB Identification: LAX08LA274
14 CFR Part 91: General Aviation
Accident occurred Friday, August 22, 2008 in North Las Vegas, NV
Probable Cause Approval Date: 07/14/2009
Aircraft: Killgore Velocity, registration: N415MK
Injuries: 3 Fatal.

NTSB investigators may not have traveled in support of this investigation and used data provided by various sources to prepare this aircraft accident report.

Shortly after takeoff from the airport, local air traffic controllers noted that the experimental amateur-built airplane was flying lower than expected, and not gaining altitude. The airplane reached a maximum altitude of about 300 feet above the ground and continued for approximately 30 seconds before descending into a residential area and impacting an occupied residence.

The accident flight was the first time the pilot had flown the airplane, and the first time the airplane took off from this particular airport. The airplane had been flown by the owner/builder for about five hours prior to the accident, and at a different airport in the area. Following the first five hours of flight, the owner/builder decided to disassemble the wings of the airplane and tow it to the accident airport because he noticed that the airplane's ground roll during the initial test flights was longer than he expected, and that oil was observed leaking from the engine cowling. The airplane was not flown again until the accident flight, and after the leaking had been corrected.

Prior to the airplane conducting any flights, it received a special airworthiness certificate as an experimental amateur-built airplane by a Federal Aviation Administration (FAA) designated airworthiness representative (DAR).

The purpose of the accident flight was to test the airplane's performance with engine boost from a noncertified, belt-driven supercharger that is normally used in automotive applications. (The supercharger had been installed by the owner/builder prior to the airplane’s certification review by the DAR; however, the accident flight was the first flight in which the supercharger control would be fully activated). The pilot had been assisting the owner/builder throughout the certification and flight testing processes.

Postaccident examination did not reveal any preimpact anomalies with the airframe. However, the examination of the engine and accessories revealed that the supercharger belt was found lodged behind the idler pulley. No signatures consistent with rotation during the impact sequence were found during examination of the supercharger, which is indicative of the belt being detached from the supercharger. Typically, supercharger belt tension is maintained through the use of an idler pulley on a sliding adjustable plate that is secured to the supercharger housing by three bolts, designed to be secured with safety wire, in 2-inch-long adjustment slots. No safety wire was found on the bolts, and one of the bolts was observed missing. Additionally,the idler plate was in a position 1/4-inch short of the most slack belt setting (i.e. 1-3/4 inches into the 2-inch adjustment toward slack), with witness marks consistent with it being in that position at impact.

The owner/builder performed a prior flight with the supercharger set to zero boost and he reported that the airplane's performance was poor. The investigation revealed that the supercharger manufacturer, in its instructions and publications, cautioned that the engine should perform like a normally aspirated engine in the event of a belt failure, but advised that ground tests should be done with the belt removed in order to simulate a failure. The manufacturer also noted that a belt failure in flight would result in a richer than normal fuel mixture, and that the pilot should compensate by adjusting the mixture in order to maintain adequate engine power. The investigation revealed that the owner/builder did not test the engine with the supercharger belt removed, and that he also had removed the idler pulley's lips in an attempt to resolve an alignment issue with the belt.

At the time of the accident, the airplane was still flying within the “Phase 1” initial flight testing operating limitations specified by the DAR who certified the airplane as experimental amateur-built. These limitations indicated that, “after a minimum time of five (5) hours” the airplane could be flown for 25 hours of operations “while based at [the accident airport]; OR, a one time flight to the "Airplane Base of Operations" may also be conducted remaining clear of all densely populated areas and congested airways”

At the time of the accident, Phase 1 flight operations for experimental aircraft at the accident airport were permitted by the FAA, after the aircraft had completed a minimum of 5 flight hours at an alternate airport, and after having demonstrated that it had met the minimum controllability requirements set forth in FAA regulations and advisory documents. About four months after the accident, the local FAA flight standards district office issued a memorandum to its inspectors to no longer permit any Phase 1 flight operations of experimental aircraft at the accident airport, or an adjacent local major airport, because the office deemed that the airports were not suitable for these types of operations, for “safety reasons”, and because they did not meet the policy in FAA Order 8130.2F which specifies that "in the case of the first flight of an aircraft from an airport surrounded by a densely populated area, but with at least one acceptable approach/departure route of flight, the FAA must ensure that the route of flight is selected which subjects the fewest persons and least property to possible hazard". The memorandum also instructed the FAA inspectors to notify their assigned DARs of this revised guidance.

The National Transportation Safety Board determines the probable cause(s) of this accident to be:

A partial loss of engine power during initial climb due to the detachment of the engine supercharger drive belt. The detachment resulted from the owner/builder's inadequate installation of the supercharger system and belt-tensioning adjustment.

Full narrative available

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