IDAHO FALLS, ID, USA
N4516K
AIR TRACTOR AT-502
AT 70 MPH ON TAKEOFF ROLL, THE AIRPLANE ENCOUNTERED A WIND SHEAR WHICH DECREASED AIRSPEED TO UNDER 60 MPH AND DROPPED THE TAIL BACK TO THE RUNWAY. THE PILOT CONTINUED THE TAKEOFF BUT SUBSEQUENTLY DID NOT ATTAIN ADEQUATE AIRSPEED TO SUSTAIN FLIGHT BEFORE REACHING THE END OF THE AIRSTRIP. HE LIFTED OFF BUT THE AIRPLANE BEGAN TO SINK IMMEDIATELY AFTER BECOMING AIRBORNE. THE AIRPLANE STRUCK A SERIES OF POWER POLES IN AN ATTEMPTED EMERGENCY LANDING ON A ROAD. AN 8 TO 10 KNOT TAILWIND EXISTED AT THE START OF THE TAKEOFF ROLL. DENSITY ALTITUDE WAS OVER 7,300 FEET. THE PILOT HAD ALSO SELECTED A GREATER TAKEOFF FLAP SETTING THAN WAS SPECIFIED BY THE AIRCRAFT FLIGHT MANUAL.
On July 24, 1995, approximately 1315 mountain daylight time, an Air Tractor AT-502, N4516K, registered to Queen Bee Air Specialties, Inc. of Rigby, Idaho, a 14 CFR 137 agricultural operator certificate holder, received substantial damage when it collided with a series of power poles in an attempted emergency landing on a road 12 miles northwest of Idaho Falls, Idaho. The event was precipitated by a reported strong gust of tailwind on takeoff roll from Queen Bee's QB One private airstrip. The commercial pilot of the single-seat agricultural aircraft elected to continue the takeoff and was subsequently unable to sustain flight after becoming airborne. He was not injured in the accident. No flight plan had been filed for the flight, a local agricultural aerial application flight conducted under 14 CFR 137. Visual meteorological conditions prevailed. The pilot stated the following in his report of the accident: At approximately 1315...I attempted a takeoff from my private airstrip...The strip is dirt surface, is oriented [true north-south] and is 3/4 of a mile in length. [NOTE: The Salt Lake City sectional aeronautical chart edition of April 27, 1995, effective on the date of the accident, lists the length of the airstrip as 2,600 feet.] The weather was scattered to broken cloud cover with some local vertically developed cumulus clouds. There was no visible precipitation or virga and no [lightning]. The wind was 8-10 mph from about 200-210 True making it about 7:30 on the tail. I loaded the hopper to about 80% full...I set to flaps to 20 degrees, checked the wind...and started the takeoff roll. All visual and gauge indications were normal and at about 3/8 of a mile into the takeoff the tail was up... ...all seemed to be going well when the airspeed sagged from above 70 mph indicated to under 60 and the tailwheel was back on the runway. I immediately started dumping my load of dry fertilizer and committed to continuing the takeoff as the runway ended in an irrigated grain field and I felt an overrun into the grain would end in an overturn with potentially disastrous results. I crossed the farmroad [1/2 mile down the runway according to a diagram submitted by the pilot with his report] with the tailwheel on the ground and even though I was holding maximum power the plane was not accelerating normally.... ...it had rained the previous day and I felt that...the surface...might allow the wheels to skid if hard braking action was used and a successful stop was not likely due to my high groundspeed and weight. I reached the end of the runway with the plane barely airborne and behind the power curve. I left wheel marks in the top of the grain for about fifty feet before getting above it but after another 150 yards I began to sink back into the grain. At this point I was trying to angle to the right so as to get onto the paved road that is parallel to and runs about 40 ft on the east side of my airstrip. I was able to get the plane out of the grainfield and onto the road but...my right wing made contact with a wood pole of a powerline that ran on the east side of the road. According to the pilot, during the landing attempt the airplane struck a series of five power poles, breaking four of them off, as the airplane traveled through a field on a path generally parallel to and to the right of the road, before he was able to bring the airplane to a stop. The airplane rolled to a stop in an upright, 3-point attitude. The pilot estimated the gross weight of the aircraft at the time of the accident as 8,980 pounds. A brochure from Air Tractor lists the AT-502's takeoff weight as 9,200 pounds in the aircraft specifications. The pilot stated that the engine functioned properly throughout the event and that no mechanical problems were involved. The 1350 surface observation at Idaho Falls, 9 miles southeast of QB One, gave conditions as: scattered clouds at 9,000 feet; visibility 60 miles; temperature 84 degrees F; wind 180 degrees magnetic at 16 knots; and altimeter setting 30.07 inches Hg, with rain showers of unknown intensity to the north and towering cumulus in all quadrants. Based on the above observation, Idaho Falls density altitude at the time of the observation was 7,318 feet. According to the Salt Lake City sectional aeronautical chart, the field elevation at Idaho Falls is 4,740 feet above mean sea level (MSL), as compared to QB One's elevation which is shown on the chart as 4,875 feet above MSL. At 1546, winds at Idaho Falls had increased to 20 knots with gusts to 34 knots. The investigator obtained extracts from the FAA-approved flight manual for the AT-502, issued February 9, 1991, from Air Tractor, Inc. The flight manual extracts, contained on Page 14 of 25, indicate the following: - "Flaps should be retracted for normal takeoff." - "Best rate of Climb speed at 8,000 lbs. take-off weight is 111 mph (IAS)...The best Rate of Climb speed at heavier weights can be expected to increase." - "TAKE-OFF (FULL HOPPER LOAD AND SHORT FIELD): Use the same procedure as for normal take-off except as follows: 1. Lower flaps to 10 [degree] position (First Mark)...." In a facsimile cover sheet accompanying the transmission of the flight manual pages, a representative of Air Tractor stated: "This plane was certified under CAM 8, so there was no requirement for [takeoff] data or climb performance."
THE PILOT'S INADEQUATE AIRSPEED AT LIFTOFF. CONTRIBUTING TO THE ACCIDENT WERE HIGH DENSITY ALTITUDE, TAILWIND CONDITIONS, THE PILOT'S SELECTION OF AN EXCESSIVE TAKEOFF FLAP SETTING, AND A WINDSHEAR ENCOUNTER.
Source: NTSB Aviation Accident Database
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