N47BA before its final flight.
|Date||October 25, 1999|
|Summary||Crew incapacitation due to decompression leading to fuel exhaustion, cause undetermined|
|Site||Edmunds County, South Dakota, U.S.|
(near Aberdeen and Mina)
|Aircraft type||Learjet 35|
|Flight origin||Orlando, Florida, U.S.|
|Destination||Dallas Love Field, Texas, U.S.|
|Fatalities||6 (all dead before crash)|
On October 25, 1999, a chartered Learjet 35 was scheduled to fly from Orlando, Florida, to Dallas, Texas. Early in the flight, the aircraft, which was climbing to its assigned altitude on autopilot, quickly lost cabin pressure and all six on board were incapacitated due to hypoxia--a lack of oxygen. The aircraft continued climbing past its assigned altitude, then failed to make the westward turn toward Dallas over north Florida and continued on its northwestern course, flying over the southern and midwestern United States for almost four hours and 1,500 miles (2,400 km). The plane ran out of fuel over South Dakota and crashed into a field near Aberdeen after an uncontrolled descent. The two pilots were Michael Kling and Stephanie Bellegarrigue. The four passengers on board were PGA golfer Payne Stewart; his agents, Van Ardan and Robert Fraley; and Bruce Borland, a golf architect with the Jack Nicklaus golf course design company.
On October 25, 1999, Learjet 35, registration N47BA, operated by Sunjet Aviation of Sanford, Florida, departed Orlando International Airport (IATA: MCO, ICAO: KMCO) at 1319Z (0919 EDT) on a two-day, five-flight trip. Before departure, the aircraft had been fueled with 5,300 lb (2,400 kg) of Jet A, enough for 4 hours and 45 minutes of flight. On board were two pilots and four passengers.
At 1327:13Z, the controller from the Jacksonville ARTCC instructed the pilot to climb and maintain flight level (FL) 390 (39,000 feet (11,900 m) above sea level). At 1327:18Z (0927:18 EDT), the pilot acknowledged the clearance by stating, "three nine zero bravo alpha." This was the last known radio transmission from the airplane, and occurred while the aircraft was passing through 23,000 feet (7,000 m). The next attempt to contact the aircraft occurred six minutes, 20 seconds later (14 minutes after departure), with the aircraft at 36,500 feet (11,100 m), and the controller's message went unacknowledged. The controller attempted to contact N47BA five more times in the next minutes, again with no answer.
About 1454Z (now 0954 CDT due to the flight's crossing into the Central Time zone), a U.S. Air Force F-16 test pilot from the 40th Flight Test Squadron at Eglin AFB in western Florida, who happened to be in the air nearby, was directed by controllers to intercept N47BA. When the fighter was about 2,000 feet (600 m) from the Learjet, at an altitude of about 46,400 feet (14,100 m), the test pilot made two radio calls to N47BA but did not receive a response. The F-16 pilot made a visual inspection of the Lear, finding no visible damage to the airplane. Both engines were running, and the plane's red rotating anti-collision beacon was on (standard operation for aircraft in flight). The fighter pilot could not see inside the passenger section of the airplane because the windows seemed to be dark. Further, he stated that the entire right cockpit windshield was opaque, as if condensation or ice covered the inside. He also indicated that the left cockpit windshield was opaque, although several sections of the center of the windshield seemed to be only thinly covered by condensation or ice; a small rectangular section of the windshield was clear, with only a small section of the glare shield visible through this area. He did not see any flight control movement. At about 1512Z, the F-16 pilot concluded his inspection of N47BA and broke formation, proceeding to Scott AFB in southwestern Illinois.
At 1613Z, almost three hours into the flight of the unresponsive Learjet, two F-16s from the 138th Fighter Wing of the Oklahoma Air National Guard (ANG), flying under the call-sign "TULSA 13 flight", were directed by the Minneapolis ARTCC to intercept. The TULSA 13 lead pilot reported that he could not see any movement in the cockpit, that the windshield was dark and that he could not tell if the windshield was iced. A few minutes later, a TULSA 13 pilot reported, "We're not seeing anything inside, could be just a dark cockpit though...he is not reacting, moving or anything like that he should be able to have seen us by now." At 1639Z, TULSA 13 left to rendezvous with a tanker for refueling.
About 1650Z, two F-16s from the 119th Wing of the North Dakota ANG with the identification "NODAK 32 flight" were directed to intercept N47BA. TULSA 13 flight also returned from refueling, and all four fighters maneuvered close to the Lear. The TULSA 13 lead pilot reported, "We've got two visuals on it. It's looking like the cockpit window is iced over and there's no displacement in any of the control surfaces as far as the ailerons or trims." About 1701Z, TULSA 13 flight returned to the tanker again, while NODAK 32 remained with N47BA.
There was some speculation in the media that military jets were prepared to shoot down the Lear if it threatened to crash in a heavily populated area. Officials at the Pentagon strongly denied that possibility. Shooting down the plane "was never an option," Air Force spokesman Captain Joe Della Vedova said, "I don't know where that came from."
The Learjet's cockpit voice recorder (CVR), which was recovered from the wreckage, contained an audio recording of the last 30 minutes of the flight (it was an older model which only recorded 30 minutes of audio; the aircraft was not equipped with a flight data recorder). At 1710:41Z, the Learjet's engines can be heard winding down, indicating that the plane's fuel had been exhausted. In addition, sounds of the stick shaker and the disconnection of the autopilot can be heard. With the engines powered down, the autopilot would have attempted to maintain altitude, causing the plane's airspeed to drop until it approached stall speed, at which point the stick shaker would have automatically engaged to warn the pilot and the autopilot would have switched itself off.
At 1711:01Z, the Lear began a right turn and descent. NODAK 32 remained to the west, while TULSA 13 broke away from the tanker and followed N47BA down. At 1711:26 CDT, the NODAK 32 lead pilot reported, "The target is descending and he is doing multiple aileron rolls, looks like he's out of control...in a severe descent, request an emergency descent to follow target." The TULSA 13 pilot reported, "It's soon to impact the ground; he is in a descending spiral."
Impact occurred approximately 1713Z, or 1213 local, after a total flight time of 3 hours, 54 minutes, with the aircraft hitting the ground at a nearly supersonic speed and an extreme angle. The Learjet crashed in South Dakota, just outside Mina in Edmunds County, on relatively flat ground and left a crater 42 feet (13 m) long, 21 feet (6.4 m) wide, and 8 feet (2.4 m) deep. None of its components remained intact.
In addition to Payne Stewart and three others, there were two pilots on board:
The 42-year-old captain, Michael Kling, held an airline transport pilot certificate and type ratings for the Boeing 707, Boeing 737, and Learjet 35. He also had Air Force experience flying the KC-135 and Boeing E-3 Sentry. Kling was also an instructor pilot on the KC-135E in the Maine Air National Guard. According to Sunjet Aviation records, the captain had accumulated a total of 4,280 hours of flight time (military and commercial) and had flown a total of 60 hours with Sunjet, 38 as a Learjet pilot-in-command and 22 as a Learjet second-in-command.
The first officer, 27-year-old Stephanie Bellegarrigue, held a commercial pilot certificate and type ratings for Learjet and Cessna Citation 500. She was also a certified flight instructor. She had accumulated a total of 1,751 hours of flight time, of which 251 hours were with Sunjet Aviation as a second-in-command and 99 as a Learjet second-in-command.
The National Transportation Safety Board (NTSB) has several levels of investigation, of which the highest is a "major" investigation. Because of the extraordinary circumstances in this crash, a major investigation was performed.
The NTSB determined that:
The probable cause of this accident was incapacitation of the flight crew members as a result of their failure to receive supplemental oxygen following a loss of cabin pressurization, for undetermined reasons.
The Board added a commentary regarding the possible reasons why the crew did not obtain supplemental oxygen:
Following the depressurization, the pilots did not receive supplemental oxygen in sufficient time and/or adequate concentration to avoid hypoxia and incapacitation. The wreckage indicated that the oxygen bottle pressure regulator/shutoff valve was open on the accident flight. Further, although one flight crew mask hose connector was found in the wreckage disconnected from its valve receptacle (the other connector was not recovered), damage to the recovered connector and both receptacles was consistent with both flight crew masks having been connected to the airplane's oxygen supply lines at the time of impact. In addition, both flight crew mask microphones were found plugged into their respective crew microphone jacks. Therefore, assuming the oxygen bottle contained an adequate supply of oxygen, supplemental oxygen should have been available to both pilots' oxygen masks.
[A] possible explanation for the failure of the pilots to receive emergency oxygen is that their ability to think and act decisively was impaired because of hypoxia before they could don their oxygen masks. No definitive evidence exists that indicates the rate at which the accident flight lost its cabin pressure; therefore, the Safety Board evaluated conditions of both rapid and gradual depressurization.
If there had been a breach in the fuselage (even a small one that could not be visually detected by the in-flight observers) or a seal failure, the cabin could have depressurized gradually, rapidly, or even explosively. Research has shown that a period of as little as 8 seconds without supplemental oxygen following rapid depressurization to about 30,000 feet (9,100 m) may cause a drop in oxygen saturation that can significantly impair cognitive functioning and increase the amount of time required to complete complex tasks.
A more gradual decompression could have resulted from other possible causes, such as a smaller leak in the pressure vessel or a closed flow control valve. Safety Board testing determined that a closed flow control valve would cause complete depressurization to the airplane's flight altitude over a period of several minutes. However, without supplemental oxygen, substantial adverse effects on cognitive and motor skills would have been expected soon after the first clear indication of decompression (the cabin altitude warning), when the cabin altitude reached 10,000 feet (3,000 m) (which could have occurred in about 30 seconds).
Investigations of other accidents in which flight crews attempted to diagnose a pressurization problem or initiate emergency pressurization instead of immediately donning oxygen masks following a cabin altitude alert have revealed that, even with a relatively gradual rate of depressurization, pilots have rapidly lost cognitive or motor abilities to effectively troubleshoot the problem or don their masks shortly thereafter. In this accident, the flight crew's failure to obtain supplemental oxygen in time to avoid incapacitation could be explained by a delay in donning oxygen masks; of only a few seconds in the case of an explosive or rapid decompression, or a slightly longer delay in the case of a gradual decompression.
In summary, the Safety Board was unable to determine why the flight crew could not, or did not, receive supplemental oxygen in sufficient time and/or adequate concentration to avoid hypoxia and incapacitation.
The NTSB report showed that the plane had several instances of maintenance work related to cabin pressure in the months leading up to the accident. The NTSB was unable to determine whether they stemmed from a common problem - replacements and repairs were documented, but not the pilot discrepancy reports that prompted them or the frequency of such reports. The report criticised Sunjet Aviation for the possibility that this would have made the problem harder to identify, track, and resolve, as well as the fact that in at least one instance the plane was flown with an unauthorized maintenance deferral for cabin pressure problems.
Stewart was ultimately headed to Houston for the 1999 Tour Championship, but planned a stop in Dallas for discussions with the athletic department of his alma mater, Southern Methodist University, about building a new home course for the school's golf program. Stewart was memorialized at the Tour Championship with a lone bagpipe player playing at the first hole at Champions Golf Club prior to the beginning of the first day of play. The owner of the crash site, after consulting the wives of Stewart and several other victims, created a memorial on about 1 acre (4,000 m2) of the site. At its center is a rock pulled from the site inscribed with the names of the victims and a Bible passage.
In 2001, Stewart was posthumously inducted into the World Golf Hall of Fame.
On June 8, 2005, a Florida state court jury in Orlando found that Learjet was not liable for the deaths of Stewart and his agents Robert Fraley and Van Ardan, who had also been aboard the plane.
The documentary series Mayday, also known by the titles Air Crash Investigation and Air Disasters, features this incident in the first episode of its 16th season. The episode, titled "Deadly Silence," was first transmitted on 7 June 2016.