The owner/pilot was participating in a fly-in to a backcountry airport in Big Creek, Idaho, that he had flown into once about two years before.
He was the last of his group to arrive in the airport vicinity, and he reported that he was using his GPS, published guidance, and information from fellow pilots to navigate to and enter the airport’s traffic pattern.
The pilot stated that on the base leg, he determined that the Cessna 182 was higher and much closer to the runway than he anticipated.
In response, he initiated a left-wing-down slip to lose altitude, and shortly thereafter, while concurrently attempting to maintain the slip, he initiated a left turn to align with the final approach path.
Almost immediately after the turn began, the airplane stalled, descended, and hit trees and terrain about 800 feet short of the runway threshold.
Although the pilot reported that he extended the flaps to 40° on the downwind leg, the flaps were found extended to 15°.
A published arrival procedure suggested a traffic pattern altitude of 800 to 1,000 feet above field elevation (AFE) and a final leg about one mile in length.
A ridge between the runway and the downwind leg limited the pilot’s view of the airport while on downwind, and the one-mile final provided an opportunity to detect airborne or ground traffic sufficiently early to allow pilots to safely compensate for the traffic.
Analysis of data from an onboard GPS device revealed that the pilot’s traffic pattern differed significantly from the published pattern. His downwind leg began at an altitude of about 800 feet AFE, but then descended continuously at a rate of about 400 feet per minute.
Also, the pilot made about a 70° turn to base leg when the airplane was abeam the threshold. Turning less than 90° resulted in a base leg oriented away from the runway and necessitated a turn of about 110° to align with the final approach course.
Further, turning early rather than continuing until the airplane was about a mile from the threshold, as suggested, put the airplane on a base leg that was very close to the runway.
Despite the descending downwind leg, the airplane’s position at the point that the pilot began his turn to final required a steep approach slope (about 10°) to arrive near the threshold in position for a normal landing.
When the pilot recognized that the plane was too high and too close to the runway to use a normal approach slope (about 4°), he could have opted to discontinue the landing attempt and execute a go-around.
However, he stated that he continued the approach because he believed that successful completion of the landing was well within his and the airplane’s capabilities.
The pilot reported that he used approach speeds similar to the airplane’s original certificated airspeeds, but the investigation was unable to determine the pilot’s actual traffic pattern airspeeds.
The investigation was also unable to determine the reason for the difference between the pilot’s reported flap setting of 40° and the as-found setting of 15°; it is possible that he began retracting the flaps after the airplane stalled.
If the flaps were set to 15° when he believed them to be at 40°, and if he was flying at the lower airspeed appropriate for the greater flap extension, this would have reduced his stall margin.
Finally, the pilot’s intentional slipping of the airplane while in the turn to final resulted in a steep, uncoordinated turn, which increased the airplane’s susceptibility to a cross-control stall.
The airplane was extensively modified from its original FAA certificated design by the installation of five significant aerodynamic or performance-related modifications that were approved through the FAA’s supplemental type certificate (STC) process.
Although this combination of STC modifications was commonly installed on the same airplane, each of the STC modifications was developed by a different company with very limited or no coordination between them.
In addition, only two of the STCs were approved by the same FAA office, and there was very limited or no coordination between any of the other FAA offices.
Although the STCs were primarily marketed as modifications that would provide short takeoff and landing capability to the airplane, the FAA-approved performance data that was provided with the STCs differed significantly from and did not support some of the advertised performance gains.
In addition, in some cases, the STCs’ pilot’s operating handbook supplements provided conflicting performance data, and there was no guidance provided regarding which performance data was applicable to the final airplane configuration.
Further, those STC modifications that were made to the airplane were frequently installed together on the same airplane, yet no definitive FAA-approved performance data was available to the pilot to operate the airplane.
Further, in this accident, the pilot could also have been motivated to operate the airplane in a manner that capitalized on the advertised performance benefits of the installed STCs.
The NTSB determined the probable cause as the pilot’s execution of a traffic pattern that did not put the airplane in position for a normal final approach and the pilot’s decision to continue the landing attempt instead of initiating a go-around, which resulted in the airplane exceeding its critical angle-of-attack and experiencing an aerodynamic stall at an altitude too low to prevent ground impact.
NTSB Identification: WPR14LA271
This June 2014 accident report is provided by the National Transportation Safety Board. Published as an educational tool, it is intended to help pilots learn from the misfortunes of others.