B-737 elevator incidents- Curt Lewis

Are the exchange of incidents and accidents unsatifactory? (Ed.)

Norway Searches For 737 Stuck-Elevator Incidents

The Accident Investigation Board Norway (AIB) is studying incidents in which pilots flying Boeing 737s for several Scandinavian airlines had to use larger-than-normal control yoke forces to unstick their aircrafts' elevators. 

The action follows two stuck-elevator investigations. One involved a Norwegian Air 737-800 that came close to stalling on approach into Finland's Kittila airport in December 2012. The other, which involved a Scandinavian Airlines 737-600 on short final to Oslo in March 2015, was tied to deicing fluid that had entered the tail section during preflight activities, and froze at altitude.

"[The] AIB is aware that in recent years, there has been a greater number of incidents involving the Boeing where it has been necessary to use larger forces on the elevator controls than normal," the Norwegian board said.

In its final report on the Oslo incident, the AIB found that the captain had to apply approximately 130 lbs. of force to "break [the elevator] loose" when he attempted to pull up the nose when flaring the aircraft for landing. Typically, pilots use 27-36 lbs. of force on the yoke to flare the aircraft, the AIB said.

Based on flight-recorder data, the AIB said the elevator became free when the aircraft was 6 ft. above the runway, and the aircraft landed normally with no damage or injuries.

The incident occurred on the same day that the AIB published its final report on the 2012 stuck-elevator incident.

The board issued several recommendations in the report to address the problem, and said the issue could potentially affect all 737 models. It included a recommendation for Boeing to perform a new risk assessment on 737 controls, and urged the FAA and EASA to ensure that Boeing performs the assessment and addresses any certification concerns.

Boeing did not agree to a new risk assessment, but did make two procedural changes. One change involves how elevator trim is set before deicing operations start. The other instructs deicing teams to apply deicing fluid from the front to the back of the elevator, and to avoid pointing the spray into the opening in the tail.

As of April, the AIB indicated it had not received responses from FAA or EASA.

As part of an investigation, the AIB performed simulations of the new Boeing procedures. It found that fluid penetration into the tail was reduced, but some still entered.

The stuck elevator survey will be mainly based on flight data recorder information from approximately 800,000 flights made by Boeing 737NGs flying for Norwegian Air Shuttle, Norwegian Air Norway and Scandinavian Airlines System, the AIB said.