FAA will mandate inspections for early models of 737 aircraft

April 5, 2011

The U.S. FAA issues an emergency directive that will require operators of specific early Boeing 737 models to conduct initial and repetitive electromagnetic inspections for fatigue damage. This action will initially apply to a total of approximately 175 aircraft worldwide, 80 of which are U.S.-registered aircraft. Most of the aircraft in the U.S. are operated by Southwest Airlines.

The FAA airworthiness directive will require initial inspections using electromagnetic, or eddy-current, technology in specific areas of the aircraft fuselage on certain Boeing 737 aircraft in the -300, -400 and -500 series that have accumulated more than 30,000 flight cycles. It will then require repetitive inspections at regular intervals.

In  November 2010, the FAA published a rule designed specifically to address widespread fatigue damage in aging aircraft. The rule requires aircraft manufacturers to establish a number of flight cycles or hours a plane can operate and be free from fatigue damage. The rule requires aircraft manufacturers to incorporate the limits into their maintenance programs.

Cracks found on three Southwest 737’s; Boeing planes Serice Bulletin

April 4, 2011

The U.S. National Transportation Safety Board (NTSB) provided an update regarding the continuing investigation into the mid-air rupture of the fuselage skin on Southwest Airlines flight 812 that occurred on Friday, April 1st. The aircraft made an emergency landing in Yuma, Arizona.

On April 3, mechanics from Southwest Airlines, under the supervision of NTSB investigators, removed a section of the ruptured fuselage skin from Friday’s accident. The segment will be transported to NTSB headquarters in Washington, D.C. for in-depth analysis.

In addition, NTSB investigators conducted additional inspections of other portions of the lap joint along the fuselage of the accident airplane and found evidence of additional cracks.

The past few days, Southwest Airlines has been conducting additional non destructive testing inspections on 79 of their 737 airplanes. Additional crack indications in the lap joints have been identified on 3 airplanes.

The NTSB, along with the other investigative parties – FAA, Boeing, and Southwest Airlines – has been working to determine what actions might be necessary to inspect any similar airplanes.
As a result of the findings to date and the results of the Southwest Airlines inspections, Boeing has indicated that they will be drafting a Service Bulletin to describe the inspection techniques that they would recommend be accomplished on similar airplanes.

While the specifics of the Service Bulletin are being developed, the focus is to require inspection of the left and right lap joints on all similar 737 airplanes that have comparable cycles (takeoffs and landings) as the accident airplane. Once the Service Bulletin is released by Boeing, the FAA will make a determination whether to make it mandatory for all similar 737 airplanes.

A check by ASN of the Service Difficulty Reports of the accident airplane, N632SW, revealed that 38 reports were related to the Fuselage (cracks, damage, corrosion of for example stringer clips and frames).

About three of those reports were from roughly the fuselage section were the rupture occorred  (Body Station 685-727).

The last report is dated March 27 at an aircraft total time of 48722 hours and 39768 cycles.

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NTSB issues safety recommendations to prevent B737 elevator jam due to FOD

February 14, 2011

The U.S. National Transportation Safety Board (NSTB) issued five safety recommendations to the Federal Aviation Administration (FAA) to prevent the elevator of certain Boeing 737 models to become jammed as a result of foreign object damage to the elevator power control unit input arm assembly.

The recommendations were issued as a result of an incident involving a Boeing 737-400 in June 2009.

On June 14, 2009, a Boeing 737-400, registration number TC-TLA, operated as Tailwind Airlines  flight OHY036, experienced an uncommanded pitch-up event at 20 feet above the ground during approach to Diyarbakir Airport (DIY), Turkey. The flight crew performed a go-around maneuver and controlled the airplane’s pitch with significant column force, full nose-down stabilizer trim, and thrust. During the second approach, the flight crew controlled the airplane and landed by inputting very forceful control column inputs to maintain pitch control. Both crewmembers sustained injuries during the go-around maneuver; none of the 159 passengers or cabin crewmembers reported injuries. The airplane was undamaged during the scheduled  commercial passenger flight.

An investigation found that the incident was caused by an uncommanded elevator deflection as a result of a left elevator power control unit (PCU) jam due to foreign object debris (FOD). The FOD was a metal roller element (about 0.2 inches long and 0.14 inches in diameter) from an elevator bearing. During  its investigation of this incident, the NTSB identified safety issues relating to the protection of the elevator PCU input arm assembly, design of the 737 elevator control system, guidance and training for 737 flight crews on a jammed elevator control system, and upset recovery training.

The National Transportation Safety Board recommends that the Federal Aviation Administration:

Require Boeing to develop a method to protect the elevator power control unit input arm assembly on 737-300 through -500 series airplanes from foreign object debris. (A-11-7)

Once Boeing has developed a method to protect the elevator power control unit input arm assembly on 737-300 through -500 series airplanes from foreign object debris as requested in Safety Recommendation A-11-7, require operators to modify their airplanes with this method of protection. (A-11-8)

Require Boeing to redesign the 737-300 through -500 series airplane elevator control system such that a single-point jam will not restrict the movement of the elevator control system and prevent continued safe flight and landing. (A-11-9)

Once the 737-300 through -500 series airplane elevator control system is redesigned as requested in Safety Recommendation A-11-9, require operators to implement the new design. (A-11-10)

Require Boeing to develop recovery strategies (for example, checklists, procedures, or memory items) for pilots of 737 airplanes that do not have a mechanical override feature for a jammed elevator in the event of a full control deflection of the elevator system and incorporate those strategies into pilot guidance. Within those recovery strategies, the consequences of removing all hydraulic power to the airplane as a response to any uncommanded control surface should be clarified. (A-11-11)


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