Wooden tongue depressors are implicated in the hard landing of a Gulfstream V last February 14 that drove the right main landing gear up through the wing, causing substantial structural damage but no injuries.
According to the NTSB, maintenance workers at General Dynamics Aviation Services (formerly a Signature maintenance center) on West Palm Beach (Fla.) International Airport put these flat wooden sticks into the landing-gear squat switches to override their function, thus simulating a gear-up configuration while the airplane is on the ground. The use of tongue depressors to make the airplane “think it’s in the air is standard practice” in the maintenance industry, according to Gulfstream. Two other manufacturers confirmed that the use of such sticks for this purpose is “fairly common.”
This procedure allows mechanics and technicians to operate and test aircraft systems and equipment that couldn’t otherwise be tested on the ground if the airplane “thinks” it’s on the ground, said Gulfstream. Gulfstream doesn’t believe that there were “remove before flight” flags on the sticks implicated in the GV incident.
Apparently, a flight crewmember or mechanic forgot to remove the sticks before the airplane took off with just the two pilots on a planned IFR flight to Teterboro (N.J.) Airport. When the crew couldn’t get the gear to retract, they decided to return to West Palm. The NTSB said that when the jet was about 50 ft over the runway entering a flare and with the thrust levers in idle, the ground spoilers deployed.
The sudden loss of lift caused the airplane to descend rapidly to the runway.
According to witnesses, the airplane “bounced high,” shearing the right main landing gear aft and pushing it up through the wing before the jet settled onto the pavement. There was no major fuel spill and the airplane did not go off the runway, according to investigators. At press time, investigators were looking into why the spoilers deployed and what effect the unremoved sticks had on making the airplane “think” it was airborne.
“If written procedures in the airplane flight manual and the instrumentation in the aircraft, which was operating as intended, had been followed, the incident could have been avoided,” said a Gulfstream spokesman. “The instruments would have indicated accurately what the status of the airplane was.” He said pilots have to follow the procedures “clearly outlined in the GV’s airplane flight manual if you get certain lights and instrument readings in the cockpit.”
The spokesman clarified, “If the airplane had been operated as intended and if written procedures by both ground and air crew had been followed, this accident could have been avoided.” The financial extent of damage had not been determined at press time, the spokesman maintained.
An FAA maintenance alerts bulletin (MAB) published soon after the accident gives further insight into the circumstances surrounding this incident. The following excerpts are from MAB No. 285:
“While changing tires, maintenance technicians placed the aircraft on jacks, and avionics personnel took advantage of this opportunity to perform tests on the electronic systems. In order to perform the tests, the avionics personnel used tongue depressors to hold the landing gear switch in the on-ground position. This procedure is commonly used for testing purposes to override the actual position of the landing gear. When the electronic tests were complete, the avionics personnel forgot to remove the tongue depressors from the gear switch. After the first takeoff, the pilot tried to retract the gear and received an unsafe landing gear indication. During landing, he placed the landing gear control in the down position, and the landing gear collapsed, causing substantial aircraft damage.”
The alert goes on to recommend “that all devices used to perform maintenance operations or to secure the aircraft be flagged and made clearly visible to anyone who may attempt to operate the aircraft. Even the switch-disabling device used in this case should have a means installed to notify an operator that the aircraft is not safe. In addition to proper flags or streamers, it would be beneficial to devise a system of placing a notice in the cockpit that could not be overlooked by a person intending to operate the aircraft.”
A few days after the incident, Gulfstream disseminated Maintenance and Operations Letter GV-MOL-02-0008, which states in part: “After any maintenance during which weight-on-wheels (WOW) switch lockout devices are used, the maintenance provider must verify that all WOW switch lockout devices have been removed…Gulfstream V preflight procedures require a check of the nose gear and main landing gear WOW switches.”
The letter concludes, “If a flight crew experiences a wow fault message during flight, the procedures in the Aircraft Flight Manual must be followed. Failure to follow the appropriate procedures for an amber wow fault crew alerting system message could result in an in-flight deployment of the ground spoilers.
There are five General Dynamics Aviation Service centers, established after the purchase of the former Signature regional maintenance facilities. The GDAC centers provide service mainly on non-Gulfstream models, although they are approved for Gulfstreams. There are also five Gulfstream Service Centers. All 10 facilities have received the FAA diamond award for excellence in quality.
The accident GV had recently changed owners (within two weeks of the accident, according to some reports). Although the airplane’s registration number is N777TY (Tyco’s airplanes use a TY suffix), it does not belong to Tyco International, according to an official at the company’s flight department in Portsmouth, N.H. The last registered owner shown for the 1996 GV (S/N 508) is BB Five of Wilmington, Del., with Bank Boston Leasing of Boston, Mass. as the operator, according to AvData of Wichita.