Advanced Preflights Are Critical After Maintenance, Part 1

The cockpit indications showed that the landing gear was down and locked at the conclusion of a post-maintenance inspection flight of a Beech BE200 Super King Air twin turboprop on Oct. 12, 2006 at Leonardtown, Maryland. However, immediately after touchdown, the landing gear warning horn sounded intermittently and the right main landing gear then collapsed, sending the aircraft out of control and off of the runway. A post-crash fire immediately erupted due to the right main landing gear penetrating the wing’s fuel tank.  

The flight crew immediately exited without injury. In contrast, substantial damage resulted to the aircraft. Examination of the left and right main landing gear assemblies revealed that both downlock plates had been installed backwards. Examination of the manufacturer’s component maintenance manual, which was used for the assembly and installation of the left and right main landing gear, revealed no guidance regarding downlock plate orientation during installation. The NTSB determined the probable cause was the airplane manufacturer's inadequate landing gear downlock plate maintenance orientation information.

Maintenance-related problems are one of the more deadly causes of accidents in general aviation according to the General Aviation Joint Steering Committee (GAJSC) and the NTSB. The parties recently renewed their emphasis on the necessity for an advanced preflight after maintenance. Incorrect servicing or installation by maintenance personnel had started the error chain that resulted in an in-flight emergency. The organizations highlight the importance of doing an advanced preflight that goes beyond the normal preflight checklist.

The FAA’s Information for Operators (InFO) #08032 entitled “Non-Routine Flight Operations” points out that proper and complete preparation before starting post-maintenance check flights needs to be more extensive than the actual flight. A review of 128 Aviation Safety Reporting System (ASRS) reports from post-maintenance preflights revealed incidents in which pilots did—and sometimes did not—detect aircraft components in a condition that would likely cause a serious in-flight malfunction.

Thirty-eight percent of the sampled ASRS reports indicated that pilots found switches or panels that had been removed and were found in the wrong position. The FAA’s Aviation Safety Team recommends developing an additional items checklist that can be used in conjunction with the aircraft’s preflight checklist for all future preflight inspections.   

Be advised that adding additional checklist items without fully understanding the proper design considerations of procedures can increase the chance of human error rather than reduce it. For instance, within the ASRS sample were instances in which the aircraft’s nosewheel collapsed during engine start because the landing gear handle position was inadvertently left in the “up” position. Practically every aircraft with retractable landing gear has a preflight checklist requiring the pilot to make certain that the landing gear lever is in the proper position, and yet this error wasn’t caught by the checklist.
   
How could a flight crew not catch the wrong position of the landing gear lever during a preflight? Expectation error is a likely explanation for oversight of such an item. Of the thousands of times that an experienced flight crew has preflighted an aircraft the landing gear handle was in the “down” position. Anytime we involve a human being in a mundane inspection process they have done many times before, it introduces the chance of this significant form of human error.
  
The FAA’s Aviation Safety Team suggests putting yourself in the right mind set and always looking over any part of the aircraft that had maintenance performed on it. You need to pay VERY close attention when preparing to fly for the first time after maintenance work.  

Common Risk Factors
NTSB Investigator Catherine Gagne has investigated a number of post-maintenance flight accidents and noted that it takes a lot of discipline for pilots to look for these types of changes and recognize them, then act.  One of the NTSB’s recommendations is to resist external pressures.  There is the desire to get the aircraft back to base to have the home mechanics look at it. Resist the pressure to “save time or money” or fear of disappointing passengers. Don’t do what is “most convenient.”

A good example of this close attention to detail and avoiding external pressure was reflected in an ASRS report. The pilot noticed that half of a rivet’s head was missing when he inspected the interior portion of the engine nacelle on a business jet. The next portion of the story reveals how external pressures can cause the error chain to propagate further.

The pilot brought the observation to the attention of his supervisor. The supervisor was focused more on the utilization of the jet and said in effect, “It sounds like the remaining half of the rivet head is working, and the adjacent rivet heads are holding the nacelle in place, so the jet is good to go.” The pilot-in-command (PIC) then conferred with an individual who had been a maintenance inspector in the military. This subject matter expert quickly pointed out that the missing half of the rivet head likely went through the engine.  

A rivet head striking compressor and turbine blades would cause an impact likely leading to a cascading failure of blades throughout the engine. The former inspector strongly urged the PIC to write up the discrepancy and provided suggestions on the maintenance manuals and FAA documents that would mandate a formal inspection of the engine for possible blade damage.   

The NTSB’s Gagne, who was the report writer for the tragic accident of a highly modified P-51D at the Reno Air Races in 2011, noted that the aircraft was exhibiting subtle indications that something wasn’t right.

“In a lot of the maintenance-related accidents that we see, the airplanes were often giving some sort of indication that something wasn’t quite right, but the pilots either didn’t detect the change or didn’t understand the significance of what they were seeing,” Gagne said. “There was a lack of vigilance on the part of the pilot for monitoring the aircraft, and maybe a lack of understanding of what they may be seeing.  Contributing to this is a pilot’s failure to identify maintenance discrepancies because of a lack of knowledge and improper techniques used during the preflight of the aircraft.” 

In Part 2 of this article, we discuss how close collaboration between maintenance personnel and pilots is vital to safely returning an aircraft to service.