FlarePath

What happened

NTSB summary, verbatim

The flight crew reported that, while in level flight, they discovered that both control columns were jammed and they could only move the control column fore and aft a maximum of about 1 inch. After running checklist procedures without success, the flight crew slowed the airplane to 180 knots and were able to regain full control of the elevator. On final approach and after configuring for landing, the elevators again seemed to be jammed. The flight crew conducted a go-around and declared an emergency. During the second approach, with both control columns partially jammed, the flight crew performed a shallow approach to a smooth landing. A postincident examination revealed that brackets holding an elevator stop had fractured, causing the elevator movement to partially jam. The fractures were consistent with fatigue failure and were caused by a combination of improperly installed shim stacks, poor alignment of the L-brackets, and cyclic stresses acting on the lower stop, which were generated by the repeated improper use of the gust lock system.

Photographs

29the aircraft, and what the investigators found

The aircraft before the accident

Wreckage and site documentation · 28 photographs from the docket

Photographs are NTSB docket attachments — works of the US government, in the public domain. Captions are the Board’s own.

Probable cause

the Board's determination

A fatigue failure of an elevator stop bracket, which resulted in a partial jam of the elevator control. Contributing to the failure was the improper installation of shim stacks, poor alignment of the brackets, and cyclic stresses acting on the lower stop, generated by the repeated improper use of the gust lock system.

Occurrence sequence

2 stepsNTSB coding · CICTT taxonomy

1 · Enroute-descent
Flight control sys malf/fail
defining event
2 · Landing
Flight control sys malf/fail

Findings

5 causal · 0 contributing

CAUSE
Aircraft › Aircraft structures › Empennage structure › Elevators — Fatigue/wear/corrosion
CAUSE
Aircraft › Aircraft structures › Empennage structure › Elevator/tab attach fitting — Malfunction
CAUSE
Aircraft › Aircraft structures › Empennage structure › Elevator/tab attach fitting — Incorrect service/maintenance
CAUSE
Aircraft › Aircraft structures › Empennage structure › Elevator/tab attach fitting — Unintentional use/operation
CAUSE
Personnel issues › Action/decision › Action › Lack of action — Not specified

Sequence of events

2 timed eventsfrom the FDR factual report · claude-fable-5-1 (in-session)

SRN 534,680-540,920 (event flight)en routep.2
Entire flight plotted in basic, flight control, miscellaneous and pitch parameter groups (figures 1-24), including the 22-lb pitch effort discretes, pitch disconnect warning, elevators L/R, control columns L/R and pitch trim; no narrative values given
previous 91 flights (figures 25-32)groundp.3
Review of all 91 recorded take-offs and landings: elevator positions at +5 deg (gust lock engaged) nine times before takeoff and eight times after landing

NTSB analysis

from the final report

The flight crew reported that, while in level flight, they discovered that both control columns were jammed and they could only move the control column fore and aft a maximum of about 1 inch. After running checklist procedures without success, the flight crew slowed the airplane to 180 knots and were able to regain full control of the elevator. On final approach and after configuring for landing, the elevators again seemed to be jammed. The flight crew conducted a go-around and declared an emergency. During the second approach, with both control columns partially jammed, the flight crew performed a shallow approach to a smooth landing. A postincident examination revealed that brackets holding an elevator stop had fractured, causing the elevator movement to partially jam. The fractures were consistent with fatigue failure and were caused by a combination of improperly installed shim stacks, poor alignment of the L-brackets, and cyclic stresses acting on the lower stop, which were generated by the repeated improper use of the gust lock system.

ATR ATR72EXECUTIVE AIRLINES INC