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BuiltByNOF

IT SHOULD NOT HAPPEN TO YOU

COMANCHE ACCIDENTS, 11.2002, And A Case

By Omri Talmon

 

Comanche Accidents, 11.2002

1.11 Date: 11/02/2002. Acft: PA-24-180. Descr: ACFT RAN OFF RWY COLLAPSED LANDING GEAR IN GRASS. Damage: Substantial. 2 POB, one not injured, one – unknown.

2.11 Date: 11/02/2002 . Acft: PA-24-180. Descr: ACFT, ON APPROACH, IMPACTED WITH TOP OF HIGH TRANSMISSION WIRE AND CRASHED INTO THE GROUND AND BURNED, 2 POB SUFFERED FATAL INJURIES, ACFT WAS DESTROYED. Damage: Destroyed. 2 POB, fatally injured.

3.11 Date: 11/07/2002. Acft: PA-30. Descr: ACFT REPORTED ELECTRICAL FAILURE JUST BEFORE TURNING FINAL. PILOT USED A HANDHELD RADIO. GEAR APPEARED DOWN. ACFT  LANDED AND ROLLED TO MIDFIELD WHEN GEAR COLLAPSED.  Damage: Minor. 4 POB, no injuries.

4.11 Date: 11/13/2002. Acft: PA-24-250. Descr.: ACFT LANDED GEAR UP. Damage: Unknown. 1 POB, no injuries.

5.11 Date: 11/13/2002. Acft: PA-24-260. Descr.: ACFT LANDED WHEELS UP. Damage: Substantial. 2 POB, no injuries.

 

A CASE

NTSB Report

Accident occurred Thursday, April 26, 2001 at FORT COLLINS, CO

Aircraft: Piper PA-39.

Injuries: 2 Serious

According to the pilot, take-off was normal, the airplane rotated at 95 mph, accelerated to 110 mph. During the initial climb, and at approximately 150 feet above ground level (agl), the left engine lost power and "quit." The pilot attempted to restart the left engine, but before he could, the right engine lost power and "quit." The pilot conducted a forced landing in a open field just north of the runway. Following touch down, the aircraft slid across two railroad tracks, impacted a ditch, struck a power pole and spun 90 degrees to the left, coming to rest on a city street. Examination of the left engine compartment found that the alternate air door was stuck in the open position, corrosion was present on the actuating cable and the cable end was broken. Examination of the right engine compartment found the alternate air door was separated from its mounting rivets and was lodged in the alternate air box, completely covering the inlet on the fuel injector servo. The pilot stated that when they arrived in Fort Collins on April 24, he had the aircraft fuel tanks topped off. According to the Fort Collins Downtown Airport daily fuel record sheet for April 24, 2001, the aircraft received 61.8 gallons of 100 low lead fuel. An examination of the remaining fuel in the airplane, and the fuel in the refueling truck, provided no evidence of fuel contamination. Six other aircraft were serviced and refueled the same day with no reported problems. A sample of an unknown substance/debris found in the left main fuel tank gascolator, was sent it to SEM-EDAX for spectra-analysis. SEM-EDAX analyzed the substance/debris and identified it as silica sand.

The National Transportation Safety Board determines the probable cause(s) of this accident as follows.

The loss of right engine power on take-off as a result of the separation of the right engine's alternate air door, which lodged in the fuel servo air inlet. A factor was the lack of suitable terrain for a forced landing.

 

 

FULL NARATIVE

On April 26, 2001, at 0830 mountain daylight time, a Piper PA-39, was substantially damaged during a forced landing after take-off from Fort Collins Downtown Airport (3V5), Fort Collins, Colorado. The commercial pilot and his passenger received serious injuries. Visual meteorological conditions prevailed. No flight plan was filed for this positioning flight being operated under Title 14 CFR Part 91. The flight was originating at the time of the accident with an intended destination of Iowa City, Iowa.

According to the pilot, when they arrived in Fort Collins on April 24, he had the aircraft fuel tanks topped off. The Fort Collins Downtown Airport daily fuel record sheet for April 24, 2001, indicated that the aircraft received 61.8 gallons of 100 low lead fuel. In the Pilot/Operator Aircraft Accident Report ( NTSB Form 6120.1/2), the pilot stated that take-off was normal, the airplane rotated at 95 mph, and accelerated to 110 mph. During the initial climb, at approximately 150 feet above ground level (agl), the left engine lost power and "quit." The pilot attempted to restart the left engine, but before he could, the right engine lost power and "quit." The pilot made a forced landing in a open field just north of the runway. The airplane struck the ground, slid over a berm and across two railroad tracks, impacted a ditch, struck a power pole, spun 90 degrees to the left, and came to rest on a city street.

Witness statements obtained by the Larimer County Sheriff's Office stated that the airplane "appeared to have just taken off" and was flying "extremely low" when it hit the ground, slid across the railroad tracks and came to a stop on the road.

According to a Colorado State Patrol Trooper, who arrived at the scene at 0838, emergency personnel were removing the pilot and passenger from the aircraft and preparing to transport them to the hospital. The trooper later interviewed the pilot and passenger at the hospital. The pilot told the trooper that his "right engine" lost power and that he went through "emergency operations," but could not gain altitude. The pilot told the trooper that he could not remember any more since he had hit his head during the crash. The passenger told the trooper that he thought the airplane lost power in the "right engine."

On May 9, 2001, a manufacturer's representative from Piper Aircraft examined the airplane and stated that the airplane was properly configured for takeoff. Control continuity was verified to the empennage surfaces. Flap position was not determined. Both fuel selectors were in the "Main" position and "Cross feed" was not selected. Some contamination was found in the fuel filters, but no blockage was noted. The landing gear was in the retracted position. The engine cowl flaps were closed. An examination of the left engine compartment found that the alternate air door was stuck in the open position, corrosion was present on the actuating cable and the cable was broken. Examination of the right engine compartment found that the alternate air door had separated from its pivoting mechanism and stuck in the fuel servo air inlet. No other indications of preimpact anomaly to the fuselage, airframe or flight surfaces were noted.

A manufacturer's representative from Textron Lycoming examined the airplane's engines and identified that the left engine exhibited no external damage other than impact damage to the propeller blades. All of the spark plugs were intact and of proper gap. The ignition wires were all attached and a spark was noted at all leads during rotation. Fuel was found in the fuel lines, engine driven fuel pump, fuel servo and nozzles. The fuel inlet screen was clean. An indication of 7 quarts of oil was noted on the dipstick/gauge. The induction system's alternate air valve door control cable end was broken off the cable. The alternate air valve was stuck in the full open/on, (non-filtered air) position. No anomalies were noted on the left engine that would have precluded its operation.

The right engine exhibited impact damage to the propeller blades and a hole in the oil sump, allowing all of the oil to drain out of the engine. All of the spark plugs were intact and of proper gap. The ignition wires were all attached and a spark was noted at all leads during rotation. Fuel was found in the fuel lines, engine driven fuel pump, fuel servo and nozzles. The fuel inlet screen was clean. An indication of 0 quarts of oil was noted on the dipstick/gauge. The induction system's alternate air valve door was separated from its mounting rivets and was lodged in the alternate air box, completely covering the inlet on the fuel injector servo. No other anomalies were noted on the right engine that would have precluded its operation.

An examination of the remaining fuel in the airplane, and the fuel in the refueling truck, provided no evidence of fuel contamination. Six other aircraft were serviced and refueled the same day with no reported problems. The manufacturer's representative from Textron Lycoming collected a sample of an unknown substance/debris found in the left main fuel tank gascolator, and sent it to SEM-EDAX for spectra-analysis. SEM-EDAX analyzed the substance/debris and identified it as silica sand.

Weather at the time of the accident, obtained from Fort Collins/Loveland Airport, located approximately 8 nautical miles at 170 degrees from the accident site was, wind, light and variable; visibility, 10 statute miles; temperature, 9 degrees Celsius; dew point, 3 degrees Celsius, altimeter setting, 30.18. The Fort Collins/Loveland Airport elevation is 5,016 feet mean sea level (msl). The calculated density altitude for Fort Collins/Loveland Airport was 5,244 feet msl.

 

MY DISCUSSION

This is a strange accident, to say the least. The pilot reported that the two engines "quit". The NTSB ignores the left engine and discusses only the right one, where a tangible reason for its failure was found. It is not up to me to discuss this issue, but several remarks are of order:

The alternate air doors are an item on the "Critical Maintenance Items for Pilots" By our Australian friends Roy Sneesby and Ken Holdsworth (this important article can be found on this web site under Maitenance). Quoting from it:

"Item: Failure of Alternate Air Box doors.

Problem: The original design of the alternate air door on the normally aspirated PA30's and PA39's puts the door downstream of the air filter and in an area of high vibration. A failure of the door hinge or shaft will lead to an immediate engine failure. A modification exists to move this door to a lower vibration area on the lid of the air filter.  If not modified, this door should be inspected thoroughly and frequently (we have had an Australian fatality due to this).

Impact: Engine failure in flight – has lead to fatalities.

Applicability: Normally Aspirated Twins."

It should be noticed that the right hand alternate air door was also in miserable shape and stuck in the open position, which means that the air was not flowing through the air filter and the engine was inhaling dust and dirt.

I have seen with my own eyes a failure of one of these alternate air doors. I was flying my PA-30 over water together with my friend Michael in his PA-39. My position was some 200 ft behind and to his right side (we flew many thousands of miles that way, with the leading aircraft calling for both as "Comanche Formation"). All of a sudden it looked like he applied brakes: His aircraft slowed down and in a second I was at his level. I throttled back and we exchanged ideas about what went wrong, as all gauges were normal. All of a sudden he started to accelerate and soon operation was normal. This repeated itself several times to our amazement. However, he was able to make it safely to destination. After landing we started to look for a possible cause and it did not take long to find that one of these doors got loose and partially blocked the air passage. When it moved back and forth the size of the free passage was changed. Fortunately, there was never a full block.

Now to the operation issue: A Twin Comanche at nearly MTOW (two POB, full fuel) at a pressure altitude of 5,244 ft does not perform miracles in terms of climbing rate with one engine inoperative, even if the aircraft is "clean" (gear and flaps up).

I guess that if I were there, taking off from a 5,300 ft runway, and one engine starts "quitting" just after rotation, I would have shut down the second one and land straight forward. There should have been enough tarmac left.

We have to realize that out of the single engine operation envelope the twin cannot fly on one engine. Further – this envelope was developed by test pilots flying factory aircraft, and we mortals who fly generation old machines, not always perfectly maintained, better take some safety margins.

 

LESSONS

The alternate air doors are a critical item of frail design which should be periodically checked and properly maintained.

The Twin drivers should be fully familiar with the envelope of the aircraft performance as a twin out of the envelope is a single with a split engine.

 

PROVERB

Remember: You are always a student in an airplane.

 

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