Washington (CNN)An Air Force reconnaissance airplane caught fire in April, endangering the lives of 27 airmen aboard the plane -- all because a retaining nut connecting oxygen tubing was not tightened properly, accident investigators have determined. The report blamed a private defense contracting company for the accident.

"Failure by L-3 Communications depot maintenance personnel to tighten a retaining nut connecting a metal oxygen tube to a junction fitting above the galley properly caused an oxygen leak. This leak created a highly flammable oxygen-rich environment that ignited," U.S. Air Force investigators wrote in report published August 3.Investigators determined the ensuing fire caused $62.4 millon in damage to the RC-135V, which electronically snoops on adversaries and relays gathered intelligence to commanders.L-3 Communications spokesman Bruce Rogowski declined comment and referred questions to the Air Force. The plane, which was about to take off on a training mission from Offutt Air Force Base in Nebraska on April 30, instead skidded to a stop on the runway. All 27 crew members made it off safely, The Omaha World-Herald reported. The World-Herald first obtained the report through a Freedom of Information Act request.U.S. sending top-line F-22 jets to EuropeThe Air Force report said the jet hit about 51 mph when the pilot aborted takeoff, well below its takeoff speed.A former pilot contacted by the World-Herald estimated that had the plane taken off, all 27 crew members could have died in an ensuing crash. "This event could have easily been that catastrophic, because of the intensity of the fire," Robert Hopkins III told the paper. "Had they taken off, it could easily have been fatal."The Air Force has 17 RC-135V/Ws in its fleet. One of them was intercepted by a Russian SU-27 jet over the Baltic Sea earlier this year in an incident that drew strong criticism from the Pentagon.The U.S. crew believed the Russian pilot's actions were "unsafe and unprofessional due to the aggressive maneuvers it performed in close proximity to their aircraft and its high rate of speed," Pentagon spokesman Mark Wright said in April.That was not the first time the U.S. has complained about an incident involving a RC-135 and a SU-27. A year earlier, a Russian jet flew within 100 feet of a RC-135 over the Sea of Okhotsk in the western Pacific, according to U.S. officials who called it "one of the most dangerous close passes in decades."

AUGUST 20, 2018 BY GENERAL AVIATION NEWS STAFF

The pilot reported that after takeoff, and about 150′ above the runway in Brunswick, Georgia, the Cirrus SR20’s engine had a total loss of power.

He further reported that a clear liquid sprayed from the upper cowling onto the windscreen.

He aborted the takeoff, landed on the runway remaining, but was unable to stop prior to the end of the runway.

The airplane skidded off the runway and hit the airport perimeter fence, which resulted in substantial damage to both wings.

During a post-accident examination, the cowling was removed, the electric fuel pump was actuated, and fuel was observed leaking from the fuel input line fitting at the fuel flow divider.

After further examination, it was revealed that the torque strip had been disturbed and the fuel line B-nut was found to be loose. After the B-nut was tightened, no fuel leaks were observed.

A review of the airplane’s engine maintenance log revealed that no recent maintenance had been performed involving the fuel pump, fuel flow divider, or associated fuel lines.

Probable cause: The total loss of engine power during takeoff due to a loose B-nut on the fuel flow divider input fuel line fitting, which resulted in a fuel leak and fuel starvation.

NTSB Identification: GAA16CA497

This August 2016 accident report is provided by the National Transportation Safety Board. Published as an educational tool, it is intended to help pilots learn from the misfortunes of others.

General Aviation News will often reprint excerpts from US National Transportation Safety Board (NTSB) accident reports, including two accidents that involved loose fuel lines after maintenance work or an inspection.

In the first accident report dated February 2010, a Piper Malibu Mirage suffered substantial damage in Nashville but luckily there were no injuries. According to the report, a 2,632-hour commercial pilot was in cruise flight when the alternator light illuminated and he smelled smoke. While diverting to the nearest airport, he lost all power on the descent but safely landed and he then noted light smoke coming from cowling for several minutes after landing.

An inspection by an FAA inspector found that the fuel control unit feed and return lines were “loose at the rear engine baffle fittings immediately above the starter and starter adapter.” A review of maintenance records showed that the starter adapter had just been replaced nine hours before the accident – meaning the mechanic had failed to properly secure the fuel control unit fuel lines.

The second accident report dated May 2010, a Piper Warrior II suffered substantial damage in Chandler (Arizona) resulting in one serious and one minor injury. According to the accident report, a private pilot and a CFI were performing touch-and-goes when smoke began to fill the cockpit – most likely coming through the defroster vents. The smoke soon became so thick that the CFI could not see outside of the windows and he ended up making a hard landing.

A review of maintenance records revealed that the last annual inspection had been completed just two days before the accident and the aircraft had flown about four hours since then. An inspection of the aircraft then revealed that the fuel line leading from the engine-driven fuel pump to the carburetor was disconnected at the fuel pump with no visible impact damage to the “B” nut on the line or to the fitting on the fuel pump – meaning the line was undone before impact. 

It was concluded that the “B” nut on the line had not been properly tightened by maintenance personnel and probably backed off due to normal engine vibration. In other words and right after maintenance, check those fuel lines!

NTSB Identification: ERA16FA27914 CFR Part 91: General AviationAccident occurred Tuesday, August 02, 2016 in Destin, FLProbable Cause Approval Date: 04/17/2018Aircraft: CESSNA 414, registration: N2735AInjuries: 1 Fatal.

NTSB investigators either traveled in support of this investigation or conducted a significant amount of investigative work without any travel, and used data obtained from various sources to prepare this aircraft accident report.

The instrument-rated commercial pilot departed from an airport adjacent to the Gulf of Mexico with an instrument flight rules clearance for a cross-country flight in dark night, visual meteorological conditions. The flight continued in a south-southwesterly direction, climbing to about 900 ft over the gulf, where it entered a steep right turn. The airplane then descended at a steep rate and impacted the water in a nose-low attitude. Postaccident examination of the recovered wreckage, including flight controls, engines, and propellers revealed no evidence of preimpact failure or malfunction.

While the outlet fuel line from the left auxiliary fuel pump was found separated and there was evidence that the B-nut was loose and had been only secured by the first 2 threads, recorded data from the engine monitor for the flight revealed no loss of power from either engine. Therefore, the final separation likely occurred during the impact sequence.

Although the accident pilot was instrument rated and had recently completed instrument currency training, the dark night conditions present at the time of the accident combined with a further lack of visual references due to the airplane's location over a large body of water, presented a situation conducive to the development of spatial disorientation. The pilot had been instructed by air traffic control to turn southwest after takeoff; however, the continuation of the turn past the intended course and the airplane's steep bank angle and excessive rate of descent are consistent with a loss of control due to spatial disorientation.

NTSB Identification: ERA17FA107

HISTORY OF FLIGHT

On February 16, 2017, about 1852 eastern standard time, a Beech A45, N3434G, collided with trees and terrain while on final approach for landing at Anderson Airport (GE21), Climax, Georgia. The private pilot was fatally injured, and the airplane was substantially damaged. The airplane was privately owned and operated by the pilot under the provisions of Title 14 Code of Federal Regulations Part 91. Night visual meteorological conditions prevailed, and no flight plan was filed for the local personal flight, which originated about 1840.

According to a friend of the pilot, the accident flight was the pilot's first flight in the airplane since the completion of an annual inspection on February 9, 2017. The friend flew the airplane from Florida to Georgia immediately after the annual inspection and reported that there were no mechanical anomalies during the flight. The friend reported that 2.2 hours of flight time accrued from the completion of the inspection to the beginning of the accident flight. According to the airplane's Hobbs meter, the duration of the accident flight was about 12 minutes.

A neighbor reported that the heard the airplane before the crash. He stated that the engine made a "sputtering" sound before impact, but that the engine did not "backfire."
AIRCRAFT INFORMATION

The single-engine, low-wing, tandem-cockpit airplane incorporated retractable, tricycle landing gear. It was equipped with a Continental IO-470-KCN reciprocating engine rated at 260 horsepower. An examination of the maintenance logbooks revealed that the engine accumulated about 1,021 hours since its last major overhaul, which was accomplished in 1983. The airplane, which was stored outside on the pilot's property, had been operated a total of 40 hours during the 11 years before the accident.

According to the maintenance records for the most recent annual inspection, the following items were marked as completed for the engine and engine bay inspection: "Check condition of fuel lines, injection unit, or carburetor," and "Check condition and age of all engine hoses."

WRECKAGE AND IMPACT INFORMATION

The fuel pump remained attached to its installation point and displayed impact damage signatures; the fuel inlet AN fitting was broken free from the fuel pump. The fuel pump was removed, and the fuel pump drive was intact; it was noted during removal that the fuel pump outlet AN "B" nut was not tight. The fuel return line from the throttle and metering unit was placed into a bucket of fuel and the drive shaft was rotated using a drill; the fuel pump was capable of pumping fuel.

The throttle and metering unit remained attached to the engine and was undamaged. The rubber coupling attaching the throttle body to the induction Y-tube exhibited dry rot signatures. The mixture and throttle control arms remained secured to their shafts and the control cable rod ends remained secured to the control arms. An examination of the fuel lines found the throttle and metering unit outlet AN "B" nut was less than finger tight. When the manifold valve cap was opened, fuel leaked from the loose throttle and metering unit outlet AN "B" nut. Compressed air was passed through the throttle and metering unit inlet fuel line; bubbles and fuel could be seen coming out of the fuel outlet AN fitting. While applying compressed air, the mixture control and throttle control were actuated and it was noted that both controls were capable of modulating the air coming out of the outlet line. The fuel outlet B-nut was removed by hand; there was no damage noted to the outlet elbow threads and the fuel line did not exhibit any impact damage. The fuel inlet screen was removed and there were no contaminants noted within the screen.

NTSB Identification: CEN17LA32814 CFR Part 91: General AviationAccident occurred Thursday, August 17, 2017 in Gonzales, LAProbable Cause Approval Date: 03/18/2019Aircraft: BEECH A36, registration: N48TZInjuries: 2 Uninjured.

NTSB investigators may not have traveled in support of this investigation and used data provided by various sources to prepare this aircraft accident report.

During the initial climb on an instructional flight, the private pilot and instructor noticed a partial loss of engine power. The pilot performed a forced landing into a hay field and the airplane nosed over. Following the accident, the mechanic who normally performed maintenance removed and discarded all twelve spark plugs, as several were worn. A subsequent examination and test run of the engine revealed a leaking fuel hose due to a loose B-nut. The loss of engine power was consistent with an inadequate fuel supply due to a fuel line leak. Further, it is likely that the worn spark plugs would also have contributed to the loss of engine power.