United Airlines Flight 173

United Airlines Flight 173 was a scheduled flight from John F. Kennedy International Airport in New York City to Portland International Airport in Portland, Oregon, with a scheduled stop in Denver, Colorado. On December 28, 1978, the McDonnell Douglas DC-8-61 operating the flight ran out of fuel while troubleshooting a landing gear problem and crashed in a suburban Portland neighborhood near NE 157th Avenue and East Burnside Street, killing 10 people on board.

The accident prompted the development of crew resource management in aviation.

Flight

Flight 173 departed from Denver's Stapleton International Airport at 15:47 MST with 189 people on board — 8 crew and 181 passengers. The estimated flight time was 2 hours and 26 minutes, and the planned arrival time in Portland was 17:13 PST, about 40 minutes after sunset. According to the automatic flight plan and monitoring system, the total amount of fuel required for the flight to Portland was 31,900 lb. About 46,700 lb of fuel was on board the aircraft when it departed the gate in Denver.

As the landing gear was being lowered on approach to Portland International Airport, the crew felt an abnormal vibration and yaw of the aircraft and a lack of an indicator light showing the gear was lowered successfully. The crew requested a holding pattern to diagnose the problem, and for about the next hour, the crew flew over southeast Portland and worked to identify the status of the landing gear and prepare for a potential emergency landing. During this time, the co-pilot and flight engineer attempted to passively alert Captain McBroom about their low fuel, a situation which was exacerbated by the fact that the gear was down with the flaps at 15° during the entire hour-long holding maneuver, significantly increasing fuel burn rate. Due to cockpit culture at the time, neither crew member adequately conveyed the seriousness of the fuel situation, leaving the captain to believe he had more fuel remaining than he actually had. As a result, the number 3 and 4 engines eventually flamed out.

As the crew prepared for a final approach for an emergency landing on runway 28L, the number one and number two engines quit due to fuel starvation flameouts, at which point a mayday was declared. This was the last radio transmission from Flight 173 to air traffic control; it crashed into a wooded section of a populated area of northeast Portland, about 6 nmi southeast of the airport, near 15845 E. Burnside Street.

Of the crew members, two were killed, flight engineer Mendenhall and lead flight attendant Joan Wheeler; two sustained injuries classified by the National Transportation Safety Board (NTSB) as "serious", and four sustained injuries classified as "minor/none". Eight passengers died, and twenty-one had serious injuries.

The 304th Aerospace Rescue and Recovery Squadron of the Air Force Reserve, based at Portland International Airport, was conducting routine training flights in the area that evening. Airborne aircraft from this unit (HH-1H Huey helicopters) were immediately diverted to the crash scene and proceeded to transport many of the survivors to local hospitals.

Crash investigation and report

The NTSB investigation revealed that, when the landing gear was lowered, a loud thump was heard. That unusual sound was accompanied by abnormal vibration and yaw of the aircraft. The right main landing gear retract cylinder assembly had failed due to corrosion, and that allowed the right gear to free fall. Although it was down and locked, the rapid and abnormal free fall of the gear damaged a microswitch so severely that it failed to complete the circuit to the cockpit green light that tells the pilots that gear is down and locked. Those unusual indications (loud noise, vibration, yaw, and no green light) led the captain to abort the landing, so he would have time to diagnose the problem and prepare the passengers for an emergency landing. While the decision to abort the landing was prudent, the accident occurred because the flight crew became so absorbed with diagnosing the problem that they failed to monitor their fuel state and calculate a time when they needed to return to land or risk fuel exhaustion.

The NTSB determined the following probable cause:

The NTSB also determined the following contributing factor:

The fuel situation was known to be on the minds of the pilot and crew to some degree. Transcripts of cockpit recordings confirm this. Media reports at the time suggested that a not widely known problem existed with fuel state gauges on that model aircraft. The problem was not widely known in part because commercial aircraft are expected to fly with no less than a 45-minute reserve of fuel at all times. The gauge problem is addressed, though obliquely, in one of the safety board's recommendations:

While the totalizer fuel gauge issue might have contributed to the crew's confusion toward the end of the flight, the NTSB report emphasized that the captain should never have allowed such a situation to develop in the first place. The NTSB made the following recommendation to specifically address that concern: