Background
The mishap aircraft, an M-28 with tail number 08-0319, was assigned to the 318th Special Operations Squadron, 27th Special Operations Wing at Cannon Air Force Base, New Mexico. The crew was deployed to the 318th Expeditionary Special Operations Squadron at Kandahar Air Base, Afghanistan.
Flight Details
On 18 December 2011 at 0939 Zulu time, the aircraft departed Kandahar Air Base on a mission to pick up four passengers at Qalat, Afghanistan, transport them to Walan Rabat short takeoff and landing zone, pick up two additional personnel from Walan Rabat, return them to Qalat, and then return to Kandahar. After an uneventful stop at Qalat to onload four passengers and their bags, the crew flew a 20-minute leg to Walan Rabat.
Surface winds at Walan Rabat were 190 degrees at 14 knots gusting to 17 knots, 30 degrees off a direct tailwind for runway 34. The landing zone has a three percent upslope for runway 34, and a 1,500-foot mountain exists 1½ miles to the north. The pilot elected to land with a tailwind on runway 34, the preferred landing direction. Walan Rabat Landing Zone is a 1,756-foot long, 31-foot wide, semi-prepared dirt strip with poorly defined boundaries, marked with AMP-3 markings (a "box-and-one" with colored panels).
The mishap pilot consulted a wind component chart and incorrectly calculated the tailwind component, mistakenly believing it was within the allowable limit for landing the M-28. The pilot flew a shallow 2½-3 degree approach due to the upsloping landing zone. At approximately 1,000 feet short of the landing zone, the pilot visually acquired the AMP-3 markings and landed at 1032 Zulu.
Accident
After a firmer than normal landing, the aircraft veered to the right and departed the prepared surface. The nose gear encountered uneven terrain and collapsed, causing the aircraft to flip tail-over-nose. The crew and passengers egressed through the copilot’s window. There were no serious injuries. The aircraft, valued at approximately $12,300,000, was destroyed. No civilian casualties occurred.
Probable Cause
The AIB president found no clear and convincing evidence of the primary cause of the accident. By a preponderance of evidence, the Landing Zone Condition, Cross-Monitoring Performance, Task/Mission-in-Progress Re-planning, Landing with an Excessive Tailwind, and Aircraft Engine Anomalies substantially contributed to the mishap, ultimately causing the aircraft to veer off the prepared surface into rough terrain, resulting in the collapse of the nose landing gear and destruction of the aircraft.