Final Report: Maintenance error leads to hard landing

 - October 15, 2007, 7:09 AM

GULFSTREAM V, WEST PALM BEACH, FLA., FEB. 14, 2002–Gulfstream N777TY was substantially damaged when it made a hard landing at West Palm Beach International Airport (PBI). The NTSB determined the probable cause was maintenance personnel’s failure to remove wooden sticks from the landing gear weight-on-wheels switches, resulting in the airplane remaining in ground mode; and the in-flight deployment of the spoilers when the flight crew moved the thrust levers to idle during the landing flare, resulting in a hard landing. The GV, which was being operated by BB Five Inc., was on a Part 91 positioning flight in VMC and on an IFR flight plan. Neither the ATP-rated pilot nor copilot, the only occupants of the aircraft, was injured.

The crew had arrived at the West Palm Beach FBO at about 5:45 a.m., performed an exterior preflight and found everything “satisfactory,” according to their statement to the FAA investigator. They also told the investigator that during taxi to the active runway they performed the before-takeoff checklists as required.

According to the cockpit voice recorder, the pilot said, “Ground spoilers, when do you want them,” and the answer was “now.” According to Gulfstream, with the ground spoilers armed, the spoilers will come up automatically whenever the thrust levers are brought to idle and the airplane is on the ground. They are armed on takeoff in case the takeoff is aborted. When the airplane gets airborne, the weight-on-wheels (WOW) switches, located on each main gear, switch to the air mode and keep the spoilers from extending in the event the pilot retards the thrust levers to idle. If the WOW switches remain in the ground mode after takeoff and the thrust levers are retarded to idle, the ground spoilers will deploy.

According to the crew’s statement, on the takeoff roll all indications were “normal,” and after liftoff the landing gear “failed to retract.” The crew performed “override procedures,” with “no change” in the indication. They then returned the landing gear lever to the “normal down position” and the checklist was completed for “landing gear failure to retract.”

They then climbed to 2,000 feet and addressed the crew alerting system message l wow & r wow pwr fail (left and right weight-on-wheels power failure), per the checklist. They reset and checked all circuit breakers with “no change in message.” They elected to return to PBI and land to evaluate the situation on the ground, and performed an ILS approach to Runway 27R.

According to the cockpit voice recorder, on final approach the pilot said, “We have three green, spoilers armed.” The crew reported that when they were on approach the thrust levers were retarded “to idle at approximately 15 feet agl…at that point the aircraft suddenly and abruptly descended to the runway with a very hard landing.”

A review of the flight-data recorder revealed the ground spoilers deployed at 57.7 feet on the radar altimeter, with a vertical acceleration of 4.25g on impact, which the cockpit voice recorder verified with the sound of the airplane hitting the runway. The copilot said, “What the…was that…know what it was…spoilers…spoilers deployed…spoilers deployed.”

According to the ATC communication transcript, after the aircraft landed the PBI tower controller asked the crew, “Where you parking?” The pilot answered, “We’re going to need a tow truck out here, we blew the right main [tire].” The tower then informed the crew that a tow truck and fire rescue were on the way. The pilot said, “We’re spilling fuel, we blew some mains and aah, we’re spilling fuel.”

According to a General Dynamics Aviation Services (GDAS) work order opened on Feb. 11, 2002, N777TY had been brought to the facility to correct the following discrepancy: “On several occasions climbing out through 2,000 feet at 225 knots indicated airspeed [we] got the overspeed warning with no other CAS messages.”

The airplane was on jacks for a tire change when a mechanic needed access to the airplane’s maintenance data acquisition unit (MDAU) to check out the overspeed problem. Since the airplane was on jacks, the mechanic had to disable the WOW switches to simulate that the WOW was in the ground mode, not in the air mode, and to gain access to the MDAU. The mechanic said he used a “popsicle stick” (the words “popsicle stick” and “tongue depressor” are used interchangeably throughout the NTSB report) to disable the WOW switches.

After the maintenance was completed, the popsicle sticks were not removed and the inspector who returned the airplane to service was not aware that the WOW switches had been disabled. Further, no notation was mentioned in the work log. A mechanic and inspector signed off the work order on February 13.

According to the FAA inspector’s statement, he arrived at the crash site on February 14 at 10 a.m. and found the airplane still on the runway. The inspector examined the wreckage and said he could see that the “right main gear had been pushed through the wing, spilling fuel.” He did not notice anything “unusual about the aircraft at this time.” He said he learned the next day “that a mechanic had removed from both main gear weight-on-wheels switches pieces of a tongue depressor used to indicate that the aircraft had weight-on-wheels while on jacks.” In addition, the FAA inspector stated the flight crewmembers “were violated for missing these pieces [tongue depressors] in the gear [during the preflight inspection], but later expunged because it was determined that a reasonable person could have missed these,” due to the fact they were hidden from view.

The investigation revealed that two employees of GDAS had gone to the wreckage about 25 minutes after the accident and started taking pictures. One of the employees asked the other while walking around the airplane “if the objects on the landing gear were normal.” According to the one employee’s statement, “…very surprised I noted the presence of tongue depressors, [and] without thinking I removed the popsicle sticks off the right gear and rushed to the other side (left landing gear) and found another tongue depressor that I also removed. I showed the findings to [the other employee], who told me to hang on to them and to inform [the operations manager] as soon as we came back to the office.”

A ground test was performed in the presence of the NTSB and FAA by General Dynamics Aircraft Service that validated the integrity of the crew alerting system. A cockpit voice recorder transcript was prepared by Gulfstream, but the pilots did not have “hot mic” selected, so only the area microphone provided a recording of intra-cockpit pilot conversation.