Accident Details
On August 26, 2009, at approximately 1835 mountain daylight time, a Piper PA-28R-200, registration N4837T, sustained substantial damage following a forced landing and collision with a tractor-trailer near Wendover, Utah. The private pilot and two passengers were not injured, nor was the truck driver. Visual meteorological conditions prevailed for the cross-country flight conducted under 14 CFR Part 91; no flight plan was filed. The flight had departed Wendover Airport (ENV) around 1830, destined for Salt Lake City International Airport (SLC).
Pilot Report
According to the pilot's statement to the NTSB, after takeoff and acceleration to 95 mph, he selected the landing gear up but observed that it did not retract. He then noticed the engine was not producing sufficient power and believed a power plant failure had occurred. The pilot pushed the mixture to full rich and leveled the airplane. He attempted to troubleshoot the landing gear by moving the gear lever down and then retrying retraction, but the gear remained extended. Two circuit breakers on the right side of the panel had popped after cycling the gear selector a second time; the pilot pushed them in and monitored. Concurrently, he began looking for an emergency landing site. He again selected gear up, but the main wheels remained extended and the warning lights were on. Deciding to land on an interstate highway, during the landing approach the left wing struck the top of a tractor-trailer, causing the airplane to yaw left and then fall to the pavement. The airplane came to rest upright facing west in the right lane of the eastbound highway. The left wing sustained substantial damage, and the left main landing gear collapsed; the nose gear and right main gear remained extended and undamaged.
Aircraft Systems
The Pilot’s Operating Manual (POM) describes a pressure sensing device that automatically lowers the landing gear regardless of selector position at airspeeds between approximately 85 and 105 mph, depending on propeller setting and altitude. This device also prevents gear retraction at airspeeds below approximately 85 mph with full power; the speed increases with power reduction or altitude increase. A manual override is provided by an emergency gear lever located between the front seats, left of the flap handle. Holding the emergency gear lever in the raised position overrides the system, allowing the gear selector to control gear position irrespective of airspeed or power. The lever has a latching device to lock it in the UP position. Piper Aircraft released Service Bulletin No. 866A on March 4, 1988, offering operators the option to either remove the emergency gear lever override system or to review and understand the relevant flight manual information. Piper considered compliance mandatory. The pilot stated he was familiar with the override system but did not attempt to use it.
Weather and Density Altitude
At the time of the accident, the weather reporting facility at ENV, about 4 nautical miles west, reported wind from 130 degrees at 7 knots, visibility 10 miles, clear sky, temperature 32°C, dew point 0°C, and altimeter setting 30.14 inches of mercury. The computed density altitude was 6,946 feet. A Piper aircraft safety investigator noted that without using the emergency override, the airspeed required for gear retraction increases by about 1 knot or mph per 1,000 feet above the base altitude of 1,000 feet msl. For a density altitude of 7,000 feet, the increase would be approximately 6 mph.
Post-Accident Examinations
On September 15, 2009, two engine runs were conducted under FAA supervision. The first run showed the engine started easily, but the mixture was sensitive. At 2,400 rpm and 20 inches of manifold pressure (MP), then 25 inches of MP, advancing the mixture caused power loss; retarding it toward idle cutoff resulted in smooth operation. The second run, after idle mixture adjustment, the engine ran smoothly only with excessive leaning near the idle cutoff. At 2,400 rpm and 25 inches of MP, power held until the mixture was advanced to full rich, whereupon rpm dropped. Replicating the accident scenario with full power (25 inches MP), propeller full forward (2,400 rpm), and mixture full rich, the engine began losing rpm as soon as the mixture was advanced. On April 6, 2010, the landing gear back-up actuator override mechanism was examined and found to have no anomalies that would preclude normal operation. Similarly, on May 6, 2010, the fuel servo (model RSA-5AD1, serial number 39040) was flow tested and showed no anomalies precluding normal operation.