Although a full report, including probable cause and contributing factors is still months away, the U.S. National Transportation Safety Board’s recently released “factual findings” indicate a Gulfstream G650 test aircraft had experienced two previous wing-drop incidents before its fatal crash on April 2, 2011, in Roswell, N.M.
The G650 — designed N652GD and the second of five test aircraft to go into service — was conducting performance tests at the Roswell airport when the plane’s right wingtip suddenly dipped on takeoff, scraping the runway.
According to the NTSB, witnesses close to the scene saw the airplane sliding on the ground with sparks and smoke and subsequent full involvement with fire while it was still moving.
The two flight-test pilots and two flight-test engineers on board survived the initial impact but were almost immediately overcome by smoke and fire and were not able to exit the aircraft.
The crew had been performing their ninth flight of the day, a heavy take-off weight field test with the right engine idle — a test used to determine the lift-off and climb-out speeds needed to develop procedures for pilots in the event of engine failure late in a take-off run.
Post-crash analyses revealed the stall angle for the aircraft to be lower than originally anticipated.
In a report to the NTSB released this week, Gulfstream indicated the company “accepts full responsibility for the accident.”
“Developmental flight test is inherently risky, but risks can and should be appropriately mitigated,” the report stated. “The causal and contributing factors described below are human errors that are best understood within the context of each individual’s duties at Gulfstream, and Gulfstream’s obligations to provide appropriate levels of support.
“As such, all actions leading to the accident are Gulfstream’s actions.”
Among the causal factors listed by Gulfstream were:
• The stall angle of attack in ground effect and the maximum coefficient of lift in ground effect were overestimated. (Ground effect refers to the increased lift and decreased drag an aircraft wing generates when it is about one wingspan’s length or less over the ground.)
• The takeoff speed schedule was not properly developed or verified, resulting in an unachievable test point for the accident run.
• Gulfstream’s internal analysis, review and approval processes did not identify those two errors prior to field performance flight testing.
• Two prior (wing drop) events in the G650 field performance program and other flight test anomalies arising from these improper speed schedules were not widely reviewed or properly understood.
In its report, Gulfstream also listed factors it believes contributed to the crash. Among them:
• The unexpected roll angle excursion may not have been initially detected and was not fully countered by the crew until just prior to initial wingtip strike. Reduction in angle-of-attack (to break the stall and restore lateral control power) was insufficient to safely fly the aircraft away, and the crew elected not to abort the takeoff (which may have been a viable option).
• The failure to reduce power after exiting the runway may have exacerbated the collisions that caused the fire.
• Turbulent air during takeoff caused the airspeed to be unsteady, which likely caused the pilot flying some difficulty achieving the target takeoff speeds.
Corrective actions
In addition to accepting full responsibility for the accident, Gulfstream’s report also indicated it would hold itself responsible for the development and implementation of corrective actions.
Following the accident, Gulfstream conducted detailed additional analysis of in-ground effect stall, the report adds. As a result, those stall characteristics are well understood and have been incorporated into the aircraft’s stall warning system. Revised speed schedules also have been developed and tested, using improved methods, and have been confirmed through flight testing as accurate.
Based on the results of the NTSB factual investigation as well as other safety reviews, Gulfstream has implemented many safety enhancements, according to the report. The company has created an Aviation Safety Officer position, reporting directly to the president of the company.
Gulfstream has also improved documentation, processes and procedures, increased support of flight test by design engineering, convened more detailed and frequent flight test safety review boards and improved onboard emergency equipment for test aircraft to better protect aircrews.
No mechanical, systems failures
With more than 200 orders for the G650 on Gulfstream’s books, the impact of the NTSB and Gulfstream reports are unclear.
Because the full NTSB report has not been released and the accident investigation is considered to be ongoing, Gulfstream officials could not comment beyond the content of their report, according to spokeswoman Heidi Fedak.
The report did stress, however, that the accident “was specific to developmental flight test and has no meaningful implications for the in-service operations of the G650.
“The investigation revealed no mechanical or systems failures whatsoever. Engines, flight controls and other components performed as expected.”
ABOUT THE JET
Scheduled for first customer deliveries in 2012, the Savannah-built G650 is Gulfstream’s flagship business jet, offering the longest range, fastest speed, largest cabin and most advanced cockpit in the Gulfstream fleet. It is capable of traveling 7,000 nautical miles at 0.85 Mach or 5,000 nautical miles at 0.90 Mach.
Using an advanced aerodynamic design, the G650 has a maximum operating speed of 0.925 Mach, which will make it the fastest civil aircraft flying. It can climb to a maximum altitude of 51,000 feet, allowing it to avoid airline-traffic congestion and adverse weather.
ON THE WEB
• To read the NTSB’s “factual findings, go to http://dms.ntsb.gov/pubdms/search/hitlist.cfm?docketID=50904&CFID=1654&C...
• To read Gulfstream’s report, go to http://dms.ntsb.gov/public%2F50500-50999%2F50904%2F493502.pdf