Every accident has its own forerunners, and every one happens either because somebody did not know where to draw the vital dividing line between the unforeseen and the unforeseeable or because well-meaning people deemed the risk acceptable.
— Stephen Barlay*
The Lockheed JetStar, powered by Garrett TFE731 turbofans, had experienced loss of one or more generators several times since undergoing a sophisticated modification to its generator control system about two weeks prior to the out and back flight between its home base at Westchester County Airport (KHPN) and Toronto International Airport (CYYZ).
Well-qualified service companies addressed the aircraft’s recurring electrical problems, yet anomalies continued. After departing KHPN en route to CYYZ, the aircraft lost all four generators for eight to nine minutes, and some basic instruments became inoperative, according to witnesses who discussed the situation with the copilot (who was also a qualified A&P mechanic) as he and the captain prepared for the return flight to KHPN.
Calls from the JetStar’s crew to their company’s Director of Maintenance apparently did not resolve the electrical issue.
Upon departing CYYZ about 15 minutes before sunset, the crew reported unspecified issues with the aircraft’s landing gear and requested a return to Toronto International. Shortly thereafter, the crew said their aircraft was OK and they would proceed to KHPN. Investigators reasoned that the problem may have related to gear retraction associated with the aircraft’s electrically driven auxiliary hydraulic pump.
The next indication that the JetStar crew was experiencing problems appeared as they neared the Brews Intersection, north of KHPN. At least six minutes prior to their anticipated arrival at Brews, New York Air Traffic Control advised the crew to hold there in anticipation of a Brews One arrival procedure for an ILS approach to KHPN. Yet the JetStart flew well past the turn point to enter the Brews holding pattern, thereby exceeding the hold protected airspace and requiring ATC to provide vectors to position the aircraft properly.
In response, the copilot stated that the JetStar had lost “the right side radio”, which probably was used to identify Brews. (The scenario described here occurred well before business aircraft were equipped with GPS.)
In addition to overflying the Brews holding pattern, the crew’s responses to ATC instructions suggested that they were preoccupied with tasks other than flying and navigating the JetStar. Further analysis by accident investigators revealed that the aircraft’s transponder was inoperative for 77 seconds as the aircraft approached the KHPN outer marker, another indication of electrical interruption.
No Room for Error
Weather at the time of the JetStar’s approach to KHPN was affected by the presence of a cold front situated about 50 miles west of the airport. Local ceilings were indefinite: 100 feet, sky obscured, visibility ranging from about one-quarter to three-quarter mile, light rain showers and variable winds at times gusting to 21 knots at the airport surface. Pilots arriving at the airport immediately before and after the JetStar reported moderate to severe turbulence throughout the approach path as well as strong wind shear. Even without the distraction of a questionable electrical system, an ILS approach to minimums at KHPN would be challenging that stormy night.
The aircraft crashed about 6,000 feet from the approach end of its intended landing runway and 2,300 feet to the right of the ILS centerline. There were no survivors.
Probable cause, according to the National Transportation Safety Board, was a distraction to the pilot at a critical time as a result of a major electrical system malfunction, which in combination with the adverse weather environment, caused an undetected deviation of the aircraft’s flightpath into the terrain.
The crew of the electrically challenged JetStar had many opportunities to say ‘No’—before the flight to CYYZ, upon landing in Toronto, and before they commenced the approach to KHPN. (The weather at an airport not far to the northwest of White Plains was experiencing significantly more favorable weather conditions.) Yet they elected to continue.
Many factors probably contributed to that decision. The challenge for all aviators is knowing when to say No.
* Extract from ‘The Final Call: Why Airline Disasters Continue to Happen’, March 1990, Stephen Barlay