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N4996V accident description

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Tail numberN4996V
Accident dateAugust 07, 1999
Aircraft typePiper PA-18-150
LocationAnaktuvuk Pass, AK
Additional details: None

NTSB description

HISTORY OF FLIGHT

On August 7, 1999, about 0600 Alaska daylight time, a tundra tire equipped Piper PA-18-150 airplane, N4996V, was destroyed by a combination of impact forces and postcrash fire when it struck mountainous terrain at 4,200 feet msl. The accident site was at 68 degrees 24.1 minutes north latitude, 148 degrees 31.8 minutes west longitude, about 74 miles northeast of Anaktuvuk Pass, Alaska, in the Brooks Mountain Range. The commercial certificated pilot, and sole passenger, sustained fatal injuries. The flight was operated by Alaskan Wilderness Ventures, of Fairbanks, Alaska. The flight was conducted under 14 CFR Part 91, as a hunter-guide business flight. The flight departed the Happy Valley airstrip, about 25 miles north of the accident site, at 0520, to spot game and drop off the passenger, prior to returning to Happy Valley to transport clients for a sheep hunt. The passenger was employed as an assistant hunting guide by the pilot. The passenger was not a pilot. He was being transported to prepare a hunting camp for clients the pilot was to fly out later in the day.

Visual meteorological conditions prevailed at the time of the accident, and a company flight plan was filed. An employee at the hunting camp said there were some clouds visible to the south, in the direction of the accident, on the morning of August 7. The closest station reporting weather was about 60 miles to the south of the accident site, and reported visual meteorological conditions with ceilings of 5,500 feet and visibility of 15 miles, between 0550 and 0750.

The flight was first reported overdue to an Alaska State Wildlife Protection Officer about 1300 on August 7. An aerial search was then commenced by the Alaska State Troopers, using a helicopter and an airplane, and another air taxi operator. The flight was reported overdue to the FAA at 0805 on August 8, by relatives of the pilot who were working at the hunting camp. The wreckage was visually located about 1300 on August 8. No Emergency Locator Transmitter (ELT) signal was received.

INJURIES TO PERSONS

Both occupants received fatal impact and thermal injuries. A postmortem examination of the pilot noted multiple injuries.

DAMAGE TO AIRCRAFT

The airplane was destroyed by a combination of impact forces and postimpact fire.

PERSONNEL INFORMATION

Pilot

The pilot held a commercial pilot certificate with ratings for single-engine land airplanes issued on April 8, 1998, and an instrument rating.

According to FAA medical and flight check applications submitted by the pilot, he had accumulated about 2,850 hours of total flight experience at the time of the accident. No records of flight time were received from the pilot's family. The NTSB investigator-in-charge (IIC) was able to verify about 500 hours of flight experience in Piper PA-18 airplanes. In the previous 90 days, the pilot had flown about 100 hours. In the previous 30 days, he had flown about 50 hours. The date of his most recent biennial flight review could not be determined.

According to an employee of the pilot/guide, the night prior to the accident, the pilot went to bed prior to 2330. According to employees of the pilot, he did not allow alcohol in camp for either employees or clients. On the day of the accident, the pilot and passenger awoke before others in camp. He departed about 0520 on the accident flight.

AIRCRAFT INFORMATION

The airplane was a 1956 Piper PA-18-150, equipped with 30-inch tundra tires. The airplane had accumulated about 5,249 hours in service at the time of the accident. The most recent annual inspection was performed on July 8, 1999, 49 hours prior to the accident.

The airplane was configured with vortex generators on the leading edge cuff of both wings, installed under Supplemental Type Certificate (STC) SA5948NM. The Airplane Flight Manual Supplement for this modification states that the stall warning vane should be adjusted to activate between 5 and 10 mph above the stall speed. The supplement does not say what that speed will be. No record was found indicating that a stall warning system was installed during initial production, nor by any subsequent modification. STC SA5948NM does not require installation of a stall warning system if it does not already exist on the airplane.

The airplane had been equipped with extended ailerons on July 10, 1993, as part of a Short Take-Off and Landing (STOL) modification installed under STC SA612AL. This modification maintained the maximum gross weight limitation at 1,750 pounds.

The airplane was modified with Wipaire Gross Weight Increase STC SA00997CH on June 30, 1999. This modification installed strengthened wing structure and approved the airplane for a maximum gross weight increase to 2,000 pounds.

The Airplane Flight Manual Supplements for both of these modifications states the airspeed indicator is to be marked at 50 mph for the lower extreme of the white arc (flap extended stall speed), and 53 mph for the low end of the green arc (flap retracted stall speed).

No information was available in the text of the STCs to define the cumulative effects of these three modifications (vortex generators, extended ailerons, increased gross weight) on the airplane's stall speed or stall performance. No information was available to determine the effects of the increased gross weight on the handling characteristics of the of the airplane with the addition of extended ailerons.

METEOROLOGICAL INFORMATION

The nearest official weather reporting station is the Automated Weather Observation System (AWOS) at Chandalar Lakes, located 60 miles south of the accident site. The weather at 0650 on the day of the accident was: winds 260 degrees at 11 knots; broken clouds at 5,500 feet, 15 miles visibility, temperature 14 degrees C, dew point 12 degrees C.

At 0750 the weather at Chandalar Lakes was: winds variable at 3 knots; broken clouds at 5,500 feet, 15 miles visibility, temperature 14 degrees C, dew point 12 degrees C.

The National Weather Service Area Forecast for the north slope of the Brooks Range, east of Anaktuvuk Pass, called for isolated broken clouds at 5,000 feet msl, and light rain showers. The outlook was VFR. The outlook for Anaktuvuk Pass, and Atigun Pass (20 miles south of the accident site) was for VFR, with occasional marginal VFR.

The winds aloft forecast for the area called for winds from the southeast between 8 and 15 knots.

One of the pilot's employees told the NTSB IIC that the morning the pilot left, the winds at camp were calm, and there were some clouds visible to the south, toward the accident site. He said the mountains (located about 15 miles south of the camp) were visible.

WRECKAGE AND IMPACT INFORMATION

The NTSB investigator-in-charge (IIC) began the on-site investigation about 1200 on August 10, accompanied by an FAA inspector, and two Alaska State Trooper pilots.

Postaccident investigation revealed that the airplane impacted in a near vertical attitude, on a rock and tundra-covered 15 degree slope, about 150 feet above the bottom of a box canyon. The airplane came to rest inverted. The nose of the airplane pointed 310 degrees magnetic, and the tail wheel was pointed 130 degrees magnetic. The left wingtip pointed 020 degrees magnetic, and the right wingtip was pointed 200 degrees magnetic.

The empennage was twisted and rotated toward the right wing

A single 3 inch deep depression was visible in the ground, extending from the tip of the right wing, to a point about 24 inches in front of the left wing tip. At the end of the left wing depression there were pieces of red glass. The right wing position light green glass remained intact. Embedded in the ground, the length of the depression, were vortex generators.

The leading edges of both wings were crushed aft 12 inches. The unburnt section of the left wing had no trailing edge damage. The left wing trailing edge flap was found in the retracted position. The right wing flap was consumed by fire.

No preaccident flight control system anomalies were noted. All cables were intact.

The right wing fuel tank, which came to rest lower than the fuselage center section, was completely consumed by fire, as was the inboard (lower section) of the left wing fuel tank. The outboard end of the left wing fuel tank was partially intact.

The engine was displaced 3 feet aft, into the front cockpit area. The propeller spinner was displaced aft to a point 6 inches ahead of the front spar of both wings. The spinner had circumferential, rotational scoring. The exhaust ducting had ductile crushing.

One propeller blade had fractured and separated 12 inches outboard of the hub, and was located under the engine. The separated blade was deformed laterally, and was torsionally twisted. A fresh scar was evident in a boulder located 3 feet in front of the engine. The scar was the same length as the broken blade section. The leading edge of both blades were gouged along the entire span.

In addition to the pilot and passenger, a rifle, a tent, a pack frame, a set of binoculars, and a small tool bag were located in the wreckage.

MEDICAL AND PATHOLOGICAL INFORMATION

A postmortem examination was performed on the pilot by the Alaska State Medical Examiner, 5700 East Tudor Avenue, Anchorage, Alaska, on August 12, 1999. The cause of death was noted to be multiple blunt force trauma. Toxicological samples were unavailable due to extensive and severe postmortem thermal change.

FIRE

The entire airplane, except for the outer two feet of the right wing, the outer 10 feet of the left wing, and the tailwheel, were involved in a postcrash fire. The fabric covering the left horizontal stabilizer surface was partially burnt. The fabric covering the vertical and right stabilizer surface was consumed.

The burn pattern extended to the outermost wing rib of the right (downhill) wing. The burn pattern extended to outer end of the left (uphill) wing fuel tank. The remainder of the left wing, outboard of the fuel tank, did not burn.

All soot patterns were developed vertically. Molten aluminum was located in puddles under the area of both wing fuel tanks. No indication of molten, spattered metal was found on the leading edges of the partially burnt sections of tail.

SURVIVAL ASPECTS

Both occupants remained strapped in their respective seats, and were involved in the postcrash fire. The four point seatbelt/shoulder harness buckles were found connected. The ELT was consumed by fire.

TESTS AND RESEARCH

The NTSB IIC estimated the takeoff weight at the beginning of the flight to be 1,822 pounds.

Disassembly of the fuel selector valve revealed the right tank position was selected at the time of the accident.

ADDITIONAL DATA/INFORMATION

The wreckage was not retained by the Safety Board. The airplane's logbooks were returned to the pilot's estate on December 28, 1999.

An NTSB Pilot/Operator Report, NTSB Form 6120.1/2 was provided to the pilot's family. This form was not returned.

(c) 2009-2011 Lee C. Baker. For informational purposes only.