Gulfstream G550 N535GA
Accident Case Study
Poor pilot decision making is not a conscious choice, of course.
Pilots don't set out to make poor decisions but there are some pilots who are poor decision makers and are predisposed to making poor decisions. In mishap report after mishap report you can almost predict the pilot in question is going to screw things up. When you pair two such pilots together, even a minor problem can become something much more severe. This is just such a mishap.
Photo: G550 N535GA Aerial view of accident site, from NTSB Accident Docket
- Date: 14 FEB 2011
- Time: 1315
- Type: Gulfstream G550
- Operator: Gulfstream Aerospace Corporation
- Registration: N535GA
- Fatalities: 0 of 2 crew, 0 of 1 passengers
- Aircraft Fate: Substantially damaged
- Phase: Landing
- Airports: (Departure) Outagamie County Regional Airport, WI (ATW/KATW), United States of America; (Destination) Outagamie County Regional Airport, WI (ATW/KATW), United States of America
Figure: N535GA Route of Flight, from flightware.com
[NTSB Factual Report, pg. 1]
- On February 14, 2011, about 1315 central standard time, a Gulfstream Aerospace Corporation GV-SP airplane, N535GA, had a landing overrun on runway 30 (6,501 feet by 150 feet, dry grooved concrete) at the Outagamie County Regional Airport (ATW), near Appleton, Wisconsin, following a reported loss of a hydraulic system. The two airline transport pilots and one passenger were not injured. The airplane incurred substantial left wing damage when the left main landing gear collapsed during the overrun.
- The airplane was registered to and operated by Gulfstream Aerospace Corporation under the provisions of 14 Code of Federal Regulations Part 91 as a maintenance test flight.
- Day, visual flight rules conditions prevailed for the flight, which operated on an activated instrument flight rules flight plan. The local flight departed from ATW about 1010.
- According to the report submitted by the operator, a preflight brief started at 0815 and some "write ups" were noted. Taxi, engine "run-ups", and takeoff were reported as normal. The flight to the Marquette, Michigan, area was normal. All inflight checks were found to be normal. However, write ups were noted with the number one flight management system, the elevator trim, and Mach trim. The autopilot disengaged during two inflight maneuvers. Following a low approach at the Austin Straubel International Airport, near Green Bay, Wisconsin, the flight crew was cleared direct to SUDIE, an initial approach fix for the area navigation (RNAV)/global positioning system (GPS) runway 30 approach at ATW.
- Flaps 10 degrees were selected prior to an intermediate fix named "APESE." Flaps 20 degrees were selected between APESE and the final approach fix (FAF) named "ZUMUG." A discussion about another approach and maintenance issues was conducted and a full stop landing was decided upon to follow the GPS approach. As the airplane approached the virtual glide slope, the pilot flying (PF) called for the landing gear to be selected down and called for the landing checklist to be conducted. The landing gear came down with an indication of three green lights and no red lights. The pilot not flying (PNF) completed the before landing checklist to "include arming ground spoilers, warning inhibit, pumping up Brakes/Hydraulics/Brake Accumulator to 3000 psi" except for "selecting full flaps." Full flaps were to be selected at the PF's call for full flaps. The PNF also selected the Landing Mode on the Cabin Pressure Controller. Subsequent to that, an amber left side hydraulic quantity low crew alerting system (CAS) message illuminated when the airplane was inside the FAF.
- The PF selected the hydraulic synoptic page and noticed the hydraulic quantity decreasing. The PF called for flaps full and PNF selected flaps full. No movement of the flaps occurred so the PNF re-selected flaps 20 degrees. Shortly after that an amber left hydraulic system fail CAS message appeared. The PNF pulled out the checklist to accomplish the procedures related to the left hydraulic system fail CAS message and suggested a go-around. At the beginning of the checklist, there is a note that, in part, indicated, "Select a runway that is at least 7,000 feet (2133.6 m) long and 150 feet (45.7 m) wide." According to the operator's report, the PF decided to land due to the significant hydraulic leak and the airplane was in a landing configuration below 1,000 feet above ground level (AGL) with prior autopilot/trim problems.
- The PNF continued to comply with the left hydraulic fail checklist and turned on the auxiliary (AUX) pump at approximately 500 feet AGL. At the beginning of the checklist, there is a caution statement to verify the availability of the auxiliary system fluid by selecting the AUX pump on for a minimum of 30 seconds to assure that pressure can be maintained. Based on flight data recorder (FDR) data, the left and right contactor transitioning from "Open" to "Closed" 26 seconds prior to all wheels on-ground, consistent with the AUX pump selected on. According to the operator's report, both the PF and PNF indicated that they thought before landing that they had a good auxiliary hydraulic system with normal spoilers, brakes, and nose wheel steering.
- The PF had throttles at idle as the airplane touched down on the runway. He indicated that it "felt it took a long time to get the nose down."
- According to the operator's report, the PF selected right thrust reverser aft. He began pressing the brakes and felt no braking action. The PF reported that he reached for the emergency brakes, saw the 3,000 feet of runway remaining sign, and decided it would not be enough remaining distance to stop. He attempted to go-around by advancing throttles to the maximum continuous thrust setting.
- The PNF felt there was not enough runway remaining to get airborne, saw the airspeed was stable at 100 knots indicated airspeed (KIAS), and did not feel acceleration or see the airspeed start to increase.
- The PNF pulled the throttles back. The PNF reported that he made this decision to avoid a worst-case scenario of a runway overrun at an even higher speed just as the engines were finally spooling up. The PNF estimated that approximately 1,000 feet of runway remained when the throttles were pulled back. At that time, the PF reached up, deployed right thrust reverser, and began steering airplane to the right to avoid obstacles. The aircraft exited the end of runway 30 at approximately 95 KIAS. The airplane veered right and came to a stop after left main landing gear collapsed.
This aircraft was owned by Paul Allen of Microsoft and just had the interior installed prior to final delivery. The pilots in question were full time pilots employed by Gulfstream. Both were former military fighter pilots but there is no evidence they had been formally trained as test pilots.
Figure: G550 Hydraulic System Schematic, from G550 Quick Reference Handbook, pg. EE-2.
In a G550 this is more serious than the name of the abnormal would indicate. The chances of hydraulic quantity being merely a little low is remote. The fluid is under high pressure and the system is pretty tight, you can go years without having to service it. If the fluid is low, it is probably on its way to zero. To make matters worse, the left system runs most of the airplane. There are two back ups, but both these can go south depending on where the leak is. The Power Transfer Unit uses right system pressure to drive left system components, but will not work if left system fluid is gone. The auxiliary pump can drive just about everything you need to land the airplane, but if the leak is in one of these components you will be relying on nitrogen to extend the landing gear (works well), the flaps will be inoperative (not a big deal with this airplane), and will be left with whatever pressure you have with the brake accumulator. The airplane can be stopped, but you need to have your act together to do this.
This makes absolutely no sense: he decided to land because he was low to the ground and knew he had a significant hydraulic leak in the landing configuration. First of all, they had planned on full flaps and didn't have that, they were not in the planned landing configuration. Secondly, and more important, they were in the process of losing the hydraulic system responsible for their brakes. Every Gulfstream pilot since the GII knows that if you have a leak in the left system (called the "combined system in the GIV and earlier) you are at risk losing the auxiliary system too.
We also have a serious CRM issue here. The checklist directs a longer runway and they had a longer runway at their disposal. The weather was good, the winds actually favored the longer runway, and they didn't have a fuel issue. The PF had no compelling reason to ignore the PNF's recommendation to go around. Further, the PNF should have been more insistent.
More about this: Crew Resource Management.
One of the complicating factors is that the hydraulic systems synoptic page can show varying amounts of fluid in the left system, which shares fluid and sits on top of the auxiliary system. Once the left system is depleted, the auxiliary system synoptic either shows full or empty, there are no intermediate indications. The auxiliary system could be intact or it could very well be the source of the leak, you don't know.
The G550 checklist has since been changed to leave the auxiliary pump alone at the point, assume it will exhaust the fluid, and land with it in the AUTO position. It will give the pilot full antiskid braking until it exhausts itself, at which point the pilot will have an easier time with the emergency brake. The fact both pilots indicated no concern about losing the normal spoilers, brakes, and nose wheel steering indicates a profound lack of systems knowledge.
This is a common sensation when the automatic ground spoilers are inoperative.
Here again a serious CRM issue. It is usually fool hardy to decide to balk a landing once the thrust reversers are out. It will take time to stow the reverser and while you are doing that it is headed for idle, further delaying spool up time for the go around.
Examination of the wreckage revealed the brake accumulator still had a full charge of 3,000 psi. The emergency brake could have brought the airplane to an uneventful stop had it been used early after landing.
Photo: G550 N535GA Landing incident runway (Gulfstream submission), from NTSB Accident Docket
It appears the leak was in the nose wheel steering system which would cause the left system fluid to be depleted and the auxiliary system to be depleted once the auxiliary pump was activated. (That would happen once the switch was turned on or if the AUTO position once any wheel brake pedal exceeded 10° deflection.)
Once the first indication of hydraulic system failure had occurred, the prudent decision would be to go around and carefully consider the ramifications. It is likely the pilots would have then realized a longer runway was necessary and the likelihood of losing brakes would require the emergency brakes.
Even after all these improper decisions, once the thrust reversers were deployed a safe stop could have been achieved using the emergency brakes. The "go" and then the "no go" indecisions sealed the aircraft's fate.
[NTSB Factual Report, pg. 1j] The National Transportation Safety Board determines that the probable cause of this accident was the captain's decision to attempt a go-around late in the landing roll with insufficient runway remaining. Contributing to the accident were (1) the pilots' poor crew coordination and lack of cockpit discipline; (2) fatigue, which likely impaired both pilots' performance; and (3) the failure of the Federal Aviation Administration (FAA) to require crew resource management (CRM) training and standard operating procedures (SOPs) for 14 CFR Part 135 operators.
Gulfstream G550 Quick Reference Handbook, GAC-AC-G550-OPS-0003, Revision 27, 24 July 2008
NTSB Factual Report Aviation, CEN11FA193, N535GA, 02/14/2011, Appleton, WI.