Close coordination and communication between maintenance personnel and knowledgeable Non-Routine Flight Operations pilots (and in some cases, manufacturer’s technical representatives) is vital to make certain an aircraft is safely returned to service and operates in the manner described in its initial type certificate. This would include a description of what was inoperative, what was repaired and what was replaced.

Clearly, pilots who fly an aircraft after any maintenance should be especially aware that components of the aircraft may have been removed, unscrewed, replaced, etc., and there exists the potential that some items may have been inadvertently overlooked.  
 
Sometimes it can be very difficult to do an adequate visual inspection of a repaired or replaced component. The need for an especially careful preflight inspection is obvious, not just of components that have been repaired and reassembled, but for items normally inspected on pre-flight inspections. The FAA recommends asking which component was removed and/or disconnected to facilitate the work performed. 

A tragic accident in the summer of 2016 reminded pilots and maintenance technicians that failure to properly secure aircraft components can compromise powerplant and control system operation, leading to system and component failures. The pilot of a Bell 407 helicopter flying for the Tennessee Valley Authority was killed during a flight to Hickory, Kentucky. During a routine landing at about 75 ft., the helicopter suddenly turned sideways, rolled and hit the ground on its right side.

Investigators found the collective lever disconnected from the pivot sleeve and its attaching hardware was found in the wreckage near the main rotor hub. The collective lever had not been safety-wired, allowing the screws to work themselves out after only 38 flight hours. The accident is a potent reminder of the importance of properly securing aircraft components with safety wire, ensuring that hardware locking mechanisms are properly installed on your aircraft, and checking them often to confirm they are taut and ready for flight.     

The FAA’s Aviation Safety Team recommends using your senses to detect anything that isn’t right. It recommends listening to the airplane, not just the engine. A good example from the Aviation Safety Reporting System (ASRS) sample occurred during a crew swap at an out-station. The outgoing captain remarked that the throttles seemed a bit stiff. During preflight the incoming pilot-in-command (PIC) moved the throttles and noted a slight extra stiffness and more importantly, heard some grinding. It was slight, but it was definitely out of the ordinary. A subsequent phone call with the maintenance controller led to a discussion about how much work it would take to explore a possible problem with a throttle cable.  

Basically, all of the seats would have to be removed from the aircraft and the floor removed so that a maintenance technician could inspect the entire path of the throttle cable. Fortunately, the PIC stood firm on this discrepancy. Maintenance technicians found the throttle cables had become dislodged from pulleys. This easily could have resulted in the throttle cables becoming stuck. 

NTSB Recommendations
The NTSB’s Catherine Gange emphasizes the importance of addressing mechanical problems before flight since it is better to handle a problem on the ground than in flight. The ASRS sample contains a good example of this. During preflight of a Cessna CE560E Citation Encore, the pilot found unusual bolts restricting the forward movement of the rudder pedals for proper adjustment.  The pilot, being quite tall, couldn’t extend the rudders to a “full forward” position based on his experience flying other CE500-series aircraft. He needed to sit “upside down” on the seat to do a closer examination of the rudder pedal mechanism.  

The pilot was perplexed to find some bolts that had been drilled into the rudder pedals to keep them from being extended forward.  This seemed very abnormal. The unusual modification was brought to the attention of maintenance technicians in the service center. To their credit, they agreed that this seemed to be unusual. Initially, the pilot and the technicians pondered if this had been an unauthorized modification. They mutually agreed to not proceed with a post-maintenance test flight until the issue was resolved.  

Hours later, after extensive research by maintenance and service center personnel, it was discovered that this was an authorized temporary change to the aircraft. It limited the rudder pedal from going too far forward and catching on a sidewall.

The NTSB also recommends sticking to the maintenance flight plan and being prepared for problems. FAA InFO 08032 recommends that pilots should determine which precautions to take and plan ahead which course of action to take if the airplane does not function in the intended manner. The agency also advises pilots to terminate the flight at the first indication that the condition has deteriorated to a point that the aircraft is no longer airworthy.

Unfortunately, a malfunction may manifest during takeoff when there is an insufficient altitude and airspeed for a safe recovery. On Nov. 21, 2003, the pilot/mechanic of a twin-engine Beechcraft Baron 55 was conducting a post-maintenance test flight at Griffin, Georgia. As the aircraft began to rotate for climb-out, the engines sounded like they began to “backfire.” The engines continued to make this sound as the aircraft climbed out. 

The Baron climbed approximately 200 ft. and the left wing pitched down. It descended under the tree line and a “loud explosion” was heard. The aircraft collided with a building a quarter of a mile from the departure end of Runway 32. A post-crash fire followed; the pilot was fatally injured.  

Review of the maintenance work order revealed that a fuel flow indicator and fuel flow transducers on the right and left engines had been installed by the pilot/mechanic prior to the flight. The fitting on the inlet side was removed and the inlet was inspected. Debris was found around the inlet orifice.  

The NTSB determined the probable cause of the crash was a loss of engine power due to the pilot’s failure to follow the engine failure emergency procedure to feather the left-engine propeller, resulting in a loss of control during climb out and the subsequent collision with a commercial building. A factor was the fuel starvation of the left engine due to debris in the fuel line.

'Check' Is Insufficient
If you want to understand the complexity of an aircraft’s assembly, you should visit an overhaul facility or an aircraft manufacturing facility to see firsthand the complexity of running control cables, electrical wiring and air conditioning vents throughout the confined structure of an aircraft’s fuselage. Even the length and composition of a screw in this confined mass needs to be carefully considered, because a screw that is too long might easily puncture a critical component, or a screw of an incompatible metal composition would cause a galvanic reaction leading to corrosion.  

The authors of pre-flight checklists are addicted to the “Windshield-check” or “Radome-check” format. The standard response of “check” does little to give specific information that pilots should examine during a thorough preflight. With no more instruction than a response of “check,” a pilot might think that the examination of the windshield is merely to make certain it doesn’t look cracked.   

In contrast, maintenance technicians and inspectors have a trained eyed on important items. They also know that catching a small crack or vibration in its earliest stages can prevent worse damage from occurring.  Aircraft maintenance manuals often contain vital information lacking in pilot preflight inspection documents.

Advanced Preflights Are Critical After Maintenance, Part 1: 
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