Incident
After a normal taxi and takeoff, the flight crew of a Gulfstream G-V found that the landing gear would not retract. After an unsuccessful manual attempt to raise the gear, the crew decided to return to the airport. During the landing flare, the ground spoilers deployed when the throttles were brought to idle. The airplane descended rapidly and landed hard, causing the right main landing gear to collapse.
Investigation
The investigation determined that a mechanic had wedged wooden sticks into the airplane's weight-on-wheels (WOW) switches to force them into the ground mode while the airplane was on jacks during maintenance. The mechanic stated that the sticks were used to disable the WOW switches to gain access to the maintenance data acquisition unit, which was necessary to troubleshoot an overspeed alert discrepancy. After the maintenance was completed, the sticks were not removed, and the airplane was returned to service without any notation about the disabled WOW switches in the work logs.
Findings
Postaccident ground testing of the cockpit crew alerting system and examination of flight data recorder (FDR) data determined that the system was functioning properly. When the accident flight conditions were recreated, the system produced a blue WOW fault message, an amber WOW fault message, and a red GND SPOILER warning message. These messages were consistent with FDR and cockpit voice recorder (CVR) information.
The G-V Quick Reference Handbook (QRH) cautions flight crews not to move thrust reverser levers and to switch the GND SPOILER armed to off following an amber WOW FAULT message. A red GND SPOILER message calls for the flight crew to disarm the ground spoilers and pull the circuit breakers to ensure the spoilers are not inadvertently rearmed. Based on CVR information, there was no indication that the flight crew followed these checklist procedures. Additionally, preflight checklist procedures called for a visual inspection of the WOW switches, which was not performed or not effective.
Ground spoilers will deploy when the throttles are brought to idle if the spoilers are armed and the WOW switches are in the ground mode. The presence of the wooden sticks kept the WOW switches in the ground mode, causing the spoilers to deploy at idle thrust.