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Accident Analysis

Preflight Follies

Take It Slow
Flight training focuses on critical skills that come into play on each and every flight. Our ability to read the weather, navigate, and make good aeronautical decisions is used every time we take to the air. While these flight skills are important, often it's what we do before ever starting the engine that determines the outcome and overall safety of a flight.

From our very first flight lesson, we're taught the importance of a thorough preflight. We verify the legal airworthiness and then check a multitude of systems that, if not in proper order, could cause problems in flight.

It was a late morning in June when the private pilot of a Cessna 182 carrying two passengers made his approach for landing at Salt Lake City International Airport in Utah. The touchdown was normal, but after the pilot lowered the nosewheel to the tarmac, it began to shimmy. Without warning, the aircraft lurched to the right, and the pilot was unable to maintain directional control with full left brake and rudder. The nosewheel collapsed, and the propeller and left wing struck the ground, causing significant damage. Neither the pilot nor his passengers were injured.

The investigation revealed that the scissors bolt on the nosewheel landing gear torque link was missing. The bolt could not be found on the runway, and there was no elongation or damage to the bolt hole to suggest that the bolt had been working loose for a period of time. While it's unclear whether the pilot could have identified the problem before the flight, the incident serves as a warning for pilots to take their time and carefully inspect their aircraft prior to takeoff. Even something as seemingly innocuous as a loose or missing fastener can have fatal consequences, as the next accident report reveals.

Before departing Centennial Airport in Englewood, Colorado, one day in early May, the pilot of a Piper Navajo (PA-31B-310) had been told of a problem with his aircraft. A mechanic had noticed several missing cowl fasteners on the aircraft and offered to replace them. The pilot indicated that he had some spare cowl fasteners and that he would take care of the problem himself.

Shortly after departure, while the airplane was climbing to cruise altitude, the left engine cowl opened, effectively forming a large scoop that created tremendous drag. The pilot struggled to control the aircraft, which witnesses reported was yawing, sputtering, and rocking back and forth. Shortly thereafter, the cowl separated entirely, striking the tail of the aircraft and damaging the flight controls. The aircraft rolled left, rolled right, and then crashed near Bennett, Colorado, destroying the aircraft and killing the pilot.

An investigation of the wreckage revealed that three primary cowl fasteners on the left engine were not properly secured and six others were missing entirely. Improper preflight, failure to maintain minimum controllable airspeed, and subsequent loss of control were listed as factors in the accident.

Other less-obvious items can be just as important to check during a preflight, such as the pitot-static system. A malfunctioning system can be a serious problem, especially during the departure phase when operating close to the ground. As one pilot writes in a NASA Aviation Safety Reporting System (ASRS) report, "Static system froze during the previous night. The airspeed indications were normal until altitude was gained. The vertical speed indicator showed no climb indication. The altimeter showed field elevation. The airspeed slowly unwound to zero. Alternate static source fixed problem....A ceiling a few feet lower would have killed us if we had tried for airspeed."

Whenever the weather is or has been below freezing, it's a good idea to activate-and then leave on-the pitot heat during preflight to remove any ice that may have accumulated and prevent melted ice from refreezing.

Sometimes when preflighting an aircraft, we fall into the trap of the blind preflight-seeing what we expect to see rather than what is really there. Ailerons moving in the wrong direction are a prime example. As a pilot reports in his ASRS report, "Upon completion of a very short flight, it was determined that the aileron controls were rigged backwards." Fortunately, the aircraft only made it 30 feet into the air before the pilot aborted the flight.

Improper preflight of the fuel system is a common theme in aircraft accidents. Without sufficient fuel or a properly operating fuel system, the flight is bound to end in disaster, as the following report demonstrates.

The pilot of a Beech Sierra (C24R) and his passenger embarked on a pleasure flight from Republic Airport in Farmingdale, New York, on a VFR January morning. Prior to the flight, the pilot had removed the fuel caps and visually checked the fuel level, but no one saw him drain fuel from either fuel tank or the main sump. The engine was running rough during the runup, so the pilot taxied back to the ramp to talk to the aircraft owner. Arriving at the ramp, the pilot and passenger remained in the aircraft with the engine running and visually scanned the ramp for the owner. They couldn't see the owner, and the engine seemed to be running smoothly again, so the pilot taxied back to the runup area. The runup was normal, and the pilot de-parted Runway 32 and entered a right downwind in the pattern.

The engine began to run rough on the downwind, then lost power completely. The pilot restarted the engine and set up for a landing. When the engine lost power again, the pilot was unable to restart it, and he set up a glide for Runway 32.

The pilot was unable to reach the runway, so he made a forced landing in a cemetery. The wings were partially separated from the fuselage in the accident, and the pilot and his passenger received minor injuries. The investigation revealed that the fuel bowl of the main sump was contaminated with water, dirt, rust, paint, and sand.

Pilots often expect an aircraft with a fresh annual inspection to be airworthy. But as the following accident report reveals, we can't let our guard down even when the aircraft has recently emerged from the hangar with a clean bill of health and the ink still wet on the maintenance records.

The Mooney M20E had received the signoff for its annual inspection only 12 days before the commercially certificated pilot purchased the aircraft. On the day of the purchase, the pilot planned to depart from Marshall County Airport in Moundsville, West Virginia, and fly VFR to Bowman Field in Louisville, Kentucky.

During the preflight, the pilot had difficulty removing the left fuel cap, which appeared to be different from the right fuel cap. The pilot took four samples of fuel from the left tank before it was free from water, but he found no contamination when sumping the right wing tank.

Soon after departure late in the afternoon, the engine started running rough, so the pilot returned and landed. Then the engine began to run smoothly, so he took off once again and headed for his destination with a friend following in another aircraft.

Approaching the Kentucky border, the pilot radioed to his friend that his fuel pressure was approaching zero, the engine was running rough, and he was going to make a precautionary landing. The pilot switched fuel tanks and proceeded to make a precautionary landing on a road. Sparks flew as the aircraft first struck power lines and then a horse trailer on the approach before landing hard on the pavement. The pilot exited the aircraft but collapsed of a heart attack about 15 minutes later.

The post-accident investigation revealed about three ounces of dirty water in the left wing tank, but found that the fuel in the right tank was clean. The boost pump was operated with the fuel injector lines disconnected, and the exiting fuel was rust-colored, containing water and a pink, paraffin-like residue.

The investigation revealed that only two tach hours had elapsed since the completion of the annual inspection. The preceding annual had been completed in November 1997, after which time the aircraft had been operated for only one hour. The annual prior to that had been completed in August 1993, with only two tach hours elapsing before the inspection in 1997.

An infrequently flown aircraft often has hidden troubles that come to light when it is airborne. Considering the suspect fuel cap, fuel contamination, and rough-running engine, the pilot should have investigated the problem and scrutinized the system further rather than committing to a cross-country flight with an aircraft of questionable airworthiness.

While sometimes we feel rushed or overconfident about our aircraft's airworthiness and our abilities, it's important to take the time to perform a thorough preflight. The few minutes we might shave from our preflight routine could add up to eternity if we miss a critical item.

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