Boeing 727-92C accident at US, 21 Nov 1980

Accident narrative

On November 21, 1980, Continental Airlines/Air Micronesia Flight 614, a Boeing 727-92C, crashed while attempting to land at Yap Airport in the Western Caroline Islands. The aircraft touched down 13 feet short of the runway, causing the right main landing gear to separate. The airplane veered off the runway and came to rest in the jungle, where a severe ground fire erupted. All 73 occupants evacuated before the aircraft was destroyed. Three people received serious injuries.

### The flight

Flight 614 was a regularly scheduled passenger and cargo trip from Saipan to Palau, with intermediate stops in Guam and Yap. The aircraft was configured with two cargo pallets forward and 78 passenger seats in the aft cabin. Aboard were 67 passengers and six crewmembers, including a company mechanic occupying the cockpit jumpseat.

The flightcrew had recently changed flying positions due to a company reduction-in-force. The captain had previously been flying as a DC-10 captain. He had not flown a B-727 in 61 days prior to the day of the accident, though he had made one landing at Saipan earlier that morning. The landing at Yap was his first unsupervised landing there. The first officer had previously been flying as a B-727 captain in domestic operations, and the second officer had been flying as a B-727 first officer.

The crew began their duty day in Guam, flew to Saipan, and then returned to Guam before departing for Yap. The en route phase and descent into the Yap area were uneventful.

### The approach and accident

At 0938, Flight 614 reported in range with Yap radio. The local weather was reported as 4,000 feet scattered, estimated 30,000 feet broken, visibility 12 miles, with a 5-knot wind from 070 degrees.

The captain, who was flying the aircraft, made an en route descent from the north and turned onto a downwind leg at the northeast portion of the airport. The downwind leg was flown at 600 feet above the runway 7 elevation to check that the runway was clear, locate the firetruck, and observe the windsock. During a portion of this leg, the captain relinquished control to the first officer to take pictures of the airport. He then resumed control, passed the camera to the second officer, and asked him to take pictures of the runway, prompting a short conversation about the camera's operation.

Abeam the approach end of runway 7, the captain began a right 90-degree and a left 270-degree turn maneuver to align the aircraft with the final approach. As the aircraft passed through 90 degrees from the runway heading, it had descended to about 300 feet above the runway elevation. When aligned with the runway heading 1.5 miles from the approach end, it was about 180 feet above the runway elevation.

Completing the turn to final at 0951:18, the first officer called, "okay, two hundred fifty feet, sink five hundred." Six seconds later, he said, "tad low." The captain increased thrust and raised the aircraft nose slightly to reduce the descent rate. The first officer subsequently called "we're at one hundred and sixty feet," "sink of three hundred," and "there's a hundred and twenty feet."

At 0951:55, the first officer called "fifty feet." Four to five seconds later, the aircraft touched down 13 feet short of runway 7. The right main landing gear immediately separated. The aircraft gradually veered off the runway, slid up over a 6- to 8-foot-high embankment where the nose gear and left main gear broke loose, and came to rest in the jungle about 1,700 feet beyond the initial touchdown.

A severe ground fire erupted immediately along the right side of the aircraft. Seventy-one occupants escaped through the two left overwing exits. The captain and the mechanic exited through the first officer's cockpit sliding window. All occupants evacuated within about one minute. Three persons sustained serious injuries: two passengers fractured bones while running from the aircraft in the jungle, and the captain fractured his collarbone and foot from the crash deceleration.

### What the investigation found

The National Transportation Safety Board found no mechanical or meteorological reasons for the short landing. The aircraft's landing weight was within limits, and flight data recorder traces showed a stabilized airspeed of about 132 knots during the final approach.

Examination of the wreckage revealed that the right main landing gear separated due to impact overload. The area where the right gear first contacted the ground had an upward slope of 4.07 degrees. The Board calculated that the aircraft's horizontal ground speed of 114.4 knots, combined with the upward sloping terrain, imparted an effective vertical speed of 824 feet per minute to the landing gear. Furthermore, the aircraft's actual vertical descent rate increased rapidly just before impact, reaching an estimated 600 to 750 feet per minute. The combination of the upslope and the high descent rate generated loads that exceeded the gear's design strength.

During postaccident interviews, the first officer, second officer, and mechanic stated they felt the final approach was low, but believed the landing would be safe after the captain increased thrust following the "tad low" callout. However, they reported that the captain retarded the throttles to idle immediately after the "fifty feet" callout, causing the rate of descent to increase rapidly. The captain stated he was aiming for a touchdown point about 300 feet beyond the threshold, rather than the company-prescribed 1,000-foot mark.

A sound spectrum analysis of the cockpit voice recorder confirmed a stable engine pitch frequency during the approach that dropped off rapidly from about 465 Hz to about 375 Hz just before the "fifty feet" callout, correlating with the crew's recollection of the power reduction.

The Board found that the captain flew a dragged-in, flat approach slope of about 1.5 degrees, rather than the standard 3-degree glidepath. Company procedures required the aircraft to be stabilized on final approach at least 500 feet above field elevation. By turning onto the final approach at 250 feet, the captain failed to establish a proper glidepath, which required excess power to maintain. When he reduced thrust to idle at 50 feet, the aircraft had insufficient thrust in relation to drag to reach the runway.

The Board evaluated the captain's training and experience. Flight managers noted that the throttle technique used by the captain was more appropriate for DC-10 landings, which permit thrust reduction to idle before touchdown without a rapid descent. In a B-727, reducing thrust to idle at 50 feet on a flat approach causes a rapid descent that cannot be overcome by stabilizer inputs. The Board believed the captain's premature thrust reduction resulted from a habit pattern developed during his previous experience flying the DC-10.

The Board also considered visual illusions. The captain reported "heat waves" rising off the trees, and the runway's ill-defined edges could create illusions of length. However, the Board concluded these were not factors, as the captain stated he intentionally aimed for the 300-foot mark and would likely have touched down there had he not reduced power when he did.

The investigation noted that the captain permitted distracting conversations and photography during the downwind leg, contrary to the company's "sterile cockpit" policy below 10,000 feet. While not a direct cause, the Board stated this illustrated a disregard for standard operating procedures.

Regarding survival aspects, the Board noted that the timely evacuation prevented fire injuries. However, the flight attendant stationed at the aft pressure bulkhead door was unable to open the aft airstair exit. She attempted to use the normal handle but was unaware of the pneumatic emergency extension system. She and several passengers were nearly trapped by thick, acrid smoke before redirecting to the overwing exits. Following the accident, the airline implemented new "hands-on" training for the emergency airstair system.

### Probable cause

The National Transportation Safety Board determined that the probable cause of the accident was "the captain's premature reduction of thrust in combination with flying a shallow approach slope angle to an improper touchdown aim point. These actions resulted in a high rate of descent and a touchdown on upward sloping terrain short of the runway threshold, which generated loads that exceeded the design strength and failed the right landing gear. Contributing to the accident were the captain's lack of recent experience in the B-727 aircraft and a transfer of his DC-10 aircraft landing habits and techniques to the operation of the B-727 aircraft."