History of the flight
The aircraft, a Piper PA-38-112 (G-BNVD), was being flown by a student on a dual cross-country flight from Carlisle to Durham Tees Valley Airport. The landing at Durham Tees Valley was firm, but not hard enough to warrant a report, and occurred without a bounce. While taxiing along the runway after completing the landing roll, the crew noticed that the left wing appeared lower than the right, initially attributed to crosswind. The aircraft was taxied at walking speed off the runway and onto the taxiway when the left main landing gear suddenly detached from the wing, causing the aircraft to stop with the left wing tip touching the ground.
Engineering examination
Examination of the detached left main landing gear revealed that one of the three attachment bolts (part number 401 511, item 22 in Figure 1) was missing. The other two bolts (part number 401 462, items 21) were attached to the landing gear with locking wire and showed clear evidence of having been pulled out of their barrel nuts as the gear detached. A search of the runway touchdown area located the missing bolt, which upon examination showed that it had unscrewed and dropped out of the barrel nut located in the wing. There was no wire locking or lock washer used, and none were specified in the aircraft's Maintenance Manual.
Maintenance
The aircraft was maintained under the CAA Light Aircraft Maintenance Schedule (LAMS) CAP 411, which requires pre-flight, daily, 50-hour, 150-hour, and annual checks. Inspection for security of the landing gear attachment bolts is required during the 150-hour and annual checks, with no requirement to take the aircraft weight off the landing gears for this check. The aircraft manufacturer's Maintenance Manual mandates pre-flight, 50-hour, 100-hour, 500-hour, 1,000-hour, and annual checks, with inspection for condition, torque, and security of the main landing gear attachment bolts required during the 100-hour, 500-hour, 1,000-hour, and annual checks.
The main landing gear attachment bolts on this aircraft were replaced during an annual check on 19 January 2006 at 5,716:50 airframe hours, using bolts specified in Piper Service Bulletin (SB) 673B. The bolts were retorqued after 24 hours with the aircraft weight on the landing gears per the Maintenance Manual. Between the annual check and the accident, two 150-hour checks had been carried out, during which the condition and security of the landing gear bolts were checked. At the time of the accident, the aircraft had flown 108 hours since the last 150-hour check.
The Piper PA-38 main landing gear attachment bolts have been subject to multiple Service Bulletins (SB 673, 673A, 673B) and Federal Aviation Administration Airworthiness Directives (AD 83-05-04 and 90-19-03), which required a one-time replacement with higher-strength bolts, barrel nuts, and saddle clamps, along with revised torquing procedures. No repetitive inspections were called for beyond the 100-hour inspection and torque check in the Maintenance Manual.
The CAA Mandatory Occurrence Report database records ten previous incidents of Piper PA-38 main landing gear attachment bolts failing or becoming loose. Five of these were reportable accidents investigated by the AAIB (Bulletins 6/85, 1/88, 12/88, 10/89, and 3/90). Following the 1989 accident to G-BMXL, the AAIB recommended that the CAA re-examine AD 83-05-04 with a view to introducing a repetitive and/or mandatory scrap life for these bolts. The CAA responded that an Additional Airworthiness Directive was being finalized but was not subsequently issued.