Colorado Aviation Accidents & Incidents

HISTORY OF FLIGHT

On October 7, 1995, at 1250 mountain daylight time, a Rupe RV-4 homebuilt, N61TR, impacted near mid field at Vance Brand Airport, Longmont, Colorado. The pilot received fatal injuries and the aircraft was destroyed by impact and postimpact fire. Visual meteorological conditions prevailed for this personal flight operating under Title 14 CFR Part 91 and no flight plan was filed. The aircraft departed Vance Brand Airport at 1215.

According to witnesses, the aircraft was passing over the airport from north to south at mid field about 800 feet above the ground and was seen to be trailing white smoke. Several witnesses described hearing a "popping" noise and saw the aircraft pitch up and then enter a left turn flat spin to the ground, impacting beside runway 11/29 about mid field facing opposite its original direction of travel. Witnesses stated the aircraft began to burn shortly after impact.

PERSONNEL INFORMATION

Pilot logbooks were retrieved from the aircraft wreckage but were damaged and no useful information was derived from them. According to available information, the pilot was, at one time, a pilot for the U. S. Air Force and stopped flying in about 1957. The pilot started flying the accident aircraft in 1993 and the aircraft logs provided information that he flew approximately 227 hours in the aircraft after he purchased it from the builder. Other flight time accumulated by the pilot is unknown.

AIRCRAFT INFORMATION

The RV-4 is an all metal low wing monoplane powered by a reciprocating engine in the 150 to 180 shaft horsepower range. Specifications are attached and the aircraft construction manual provided information that a wood propeller was standard.

The RV construction manual states the following concerning the use of metal propellers:

"Ideally, a fixed pitch metal prop would have some advantages over a fixed pitch wood prop. But all of the fixed pitch metal props manufactured were designed for much slower airplanes so their pitch angles are much too low to be effective at the RV-4's cruise speed. While it is true that metal props can be re-pitched for more or less speed, they cannot be re-pitched to the extent needed for the RV-4.

In addition to a loss of efficiency incurred through excessive re-pitching, the stress on the metal renders them unsafe for use. The stresses on metal props are very involved, and the most insidious of these are harmonic vibration stresses which are not detectable through vibrations which can be felt by the pilot. Extensively reworked metal props have a history of losing sections of their blades which can (and have, with fatal results) easily result in catastrophic imbalances capable of tearing the engine completely free of the mount and airframe. This is but a superficial explanation, it gives some idea why fixed pitch metal props were not considered suitable for use o