B-2A accident investigation board

Flying Safety, August, 2003

Editors Note: This report is presented to help you prevent like mistakes in your unit. Not all sections of the AIB report are listed in this article due to privacy concerns and relevance to the cause of the mishap. If you need to see the entire report, please see your Wing Chief of Safety.

EXECUTIVE SUMMARY

The left main landing gear on a B-2A collapsed while the B-2A was undergoing non-routine diagnostic maintenance on the left main landing gear to eliminate false computer indications of the gear's position. Five maintenance personnel were under the aircraft when it collapsed and were injured. Aircraft damage from the mishap included the left main landing gear, the left weapons bay and main gear doors, the left wing and its control surfaces and a yet to be determined amount of internal structural damage. Shortly before the gear collapsed, maintenance personnel were removing gear indication sensor components on the left main landing gear.

The primary cause of the mishap was improper maintenance practices not sanctioned in the aircraft technical orders and maintenance job guides. The AIB determined that a main landing gear safety pin was improperly removed by one of the maintenance personnel, followed by the same individual pushing up the lock-link assembly into an unsafe retracted condition. Without hydraulic power, the aircraft collapsed under its own weight. Material failure and design flaws were ruled out as possible contributing factors.

5. MAINTENANCE

a. Forms Documentation.

At the time of the mishap, the 781 forms for the mishap aircraft were in the dock with the aircraft as required. Both the 781 forms and CAMS were reviewed and found to be current and accurate for the mishap aircraft. Specifically, all immediate, urgent, and routine Time Compliance Technical Orders were accomplished with no noted problems. Weight and balance records show the weight of the aircraft with a specific fuel load and internal stores (armament) as well as the center of gravity for the aircraft in its current configuration. All weight and balance records were current and accurate.

c. Maintenance Procedures.

After reviewing the maintenance and training records, the maintenance procedure being performed at the time of the gear collapse was determined to be the cause of the mishap.

d. Maintenance Personnel and Supervision.

The AIB thoroughly reviewed all pertinent training records, maintenance procedures, practices, and performance. Each member of the maintenance career field has a set of training records, which includes the Career Field Education and Training Plan (CFETP). Each maintenance member will have a plan in his or her records and it is supposed to indicate Air Force, ACC, and work center requirements. Any work that a member is performing must be indicated in their training records. For each maintenance shop, there is a master CFEPT. The master CFEPT lists all training requirements for each work center, and it is to be used as the training guideline that each member is supposed to follow.

Training documentation throughout the Aero Repair (A/R) shop was inconsistent with current training guidelines. Specifically, the A/R shop's master CFEPT included most of the duties of an A/R Technician; however, it does not specify troubleshooting or rigging and adjustment of the main landing gear as a training requirement for technicians seeking to upgrade their training to a higher skill level, nor is this procedure listed as an option for training. Items necessary are marked with a circle. Thus, there is a whole set of tasks that A/R technicians are required to perform, and are performing on a routine basis, that are not required in the Master CFETP. Ultimately, this omission led to incomplete and inadequate training. Throughout the Air Force, maintenance personnel are prohibited from performing tasks on which they have not been trained, regardless of the adequacy of training documentation.

f. Unscheduled Maintenance.

The B-2A aircraft is highly computerized. It has sensors that tell an onboard computer when the landing gear is fully retracted in the wheel well and when the gear is fully extended for landing. On a previous sortie, the aircrew reported that the left main landing gear (MLG) was slower to retract than the right upon takeoff, and that it would not retract at all after the first touch and go. Maintenance inspection revealed that the left MLG's truck position actuator (TPA) lower mount bolt was broken. The TPA is the component that stows the tires in an up position, which then allows the landing gear to retract into the wheel well. TPA bolt is located inside the main landing gear and cannot be repaired without taking the landing gear apart. Thus, the landing gear had to be removed and sent to a central depot maintenance facility, and an entire new landing gear had to be installed on the aircraft.

After the gear change, the aircraft flew four times with no reported discrepancies for the left MLG. However, on the last sortie before the mishap, the onboard computer reported two errors. The left main landing gear was two-to-four seconds slower than the right, and the left main landing gear proximity sensors indicated a temporary failure-to-lock indication. After one second, the failure indication cleared. Following these errors, a tiger team was formed at the request of the bomb squadron, to perform troubleshooting of the problems. It was decided, at a meeting, that the focus of the troubleshooting would be the failures of the proximity sensors and not the slow retraction problem, because although the main landing gear was slower than the right, it still retracted within technical order guidance timing.