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On May 7, 2005, at 1637 mountain standard time, a Cessna 172RG, N4970V, settled back to the ground during an attempted takeoff from the Grand Canyon National Park Airport, Grand Canyon, Arizona. The accident location is in a field about 1 mile south of the airport. Grey Eagle Aviation, Inc., the registered owner of the airplane, was operating it under the provisions of 14 CFR Part 91. The private pilot and two passengers sustained minor injuries; the airplane sustained substantial damage. Visual meteorological conditions prevailed and a visual flight rules flight plan was filed but not yet activated. The flight was destined for Palomar Airport, Carlsbad, California, and was originating at the time of the accident. The pilot had flown the airplane to the Grand Canyon from Carlsbad earlier that day.
According to witnesses, the airplane was departing runway 21. When the main gear lifted from the runway's surface, the airplane flew in ground effect but did not climb. It proceeded down the runway without climbing prior to settling to the ground in a field. During the ground impact, the left wing collapsed downward at its root and the airplane nosed down.
During a telephone conversation with the pilot a few days following the accident, the pilot reported that the airplane would not climb during takeoff. After the airplane left the runway's surface, he retracted the landing gear in an attempt to increase the climb rate. The airplane settled toward the ground. The pilot attempted to land on the remaining runway and extended the gear. By the time the gear was extended, there was not enough usable runway to land the airplane. He then maneuvered the airplane to avoid trees and force-landed the airplane in the terrain. The mixture was set in the full-rich (forward) position. No control or power anomalies were noted with the airplane on the flight to the Grand Canyon earlier that day.
In a written statement submitted to a National Transportation Safety Board investigator on May 13, the pilot and his passengers said they departed Carlsbad without incident. He recalled the tachometer at take off being just over 2,500 revolutions per minute. Once established in the climb at 83 knots, he set 2,500 rpm and 25 inches manifold pressure as he had been instructed during his recent check flight with Grey Eagle Aviation.
The takeoff felt normal and the takeoff distance seemed "fairly" normal, possibly a little longer than his previous flights from Carlsbad. The airplane appeared to climb satisfactorily and he had no problems climbing to 10,000 feet. During cruise, there were brief periods with some roughness from the engine. However, the temperatures and pressures all seemed normal during these occasions and the pilot was not concerned over continuation of this flight. The roughness was unaffected by variation of the mixture selected or the altitudes at which he flew.
Once established in the cruise he leaned the mixture. When adjusting the mixture and throttle, he was not able to achieve 2,700 rpm and used 2,400 to 2,500 rpm maximum and 20 to 21 inches manifold pressure at cruise. Initially, he did not think too much about the maximum rpm achievable. He later recalled thinking about the decreased performance and the occasional roughness during the flight, and referred to the Pilot's Operating Handbook (POH) a couple of times during the flight to confirm the rpm and manifold pressure values.
Prior to his arrival at Grand Canyon Airport, the pilot reconfirmed his takeoff performance calculations because he wanted to know how much fuel to take on. He reviewed his flight guide and again noted the runway length, the airport altitude, and the temperature from the automated terminal information service (ATIS). He referred to the POH takeoff charts using 8,000 feet and 20 degrees Celsius and this suggested the distance to 50 feet would be 4,440 feet, and the predicted rate of climb to be around 400 feet per minute. Performance calculations indicated that with the gross weight near the specified maximum, the airplane would need about 4,500 feet to take off.
The pilot further stated that the taxi and run-up just prior to the accident flight were uneventful. As the airplane began gaining speed on runway 21, it lifted from the runway; however, it would not climb. No unusual sounds were noted. The pilot then retracted the landing gear in hopes of attaining a better climb performance. When the landing gear retracted, the airplane sank and would not climb. The pilot then decided to abort the takeoff and extend the landing gear. By the time the landing gear was down-and-locked, there was no usable runway landing surface available. The pilot continued flying the airplane at a low altitude, while altering his course to the left in an effort to prevent impact with trees. The pilot then force landed the airplane in a field. Prior to takeoff, the flaps were retracted and the mixture control was in the full forward (rich) position.
The pilot further stated that during his training, he used an airplane weight of 1,624 pounds while completing a weight and balance calculation. He reported that his instructor said that this airplane weight was okay to use and that this was similar to the actual weight of the airplane as given in the weight and balance statement. Because of this understanding, the pilot used the airplane weight of 1,624 pounds on all of his weight and balance calculations for the airplane. The pilot calculated the airplane's takeoff weight to be 2,650.2 pounds using an airplane weight of 1,624 pounds and a baggage weight of 15 pounds.
In a later statement sent to the Safety Board investigator on August 23, the pilot reported that the mixture was leaned prior to departure from the airport. After speaking with a Federal Aviation Administration (FAA) inspector regarding a flight assessment test, the pilot thought about the original statement he made regarding the circumstances of the accident. The pilot stated that he moved the engine, propeller, and mixture controls forward following the accident when he was retrieving personal items from the airplane. In his original notes written just after the accident he noted, "Mixture- rich side of lean at T-off [takeoff]", which is why he wrote "rich" in his written report. In this message, the pilot also reported that he had notated, "mixture leaned (in climb)- no significant improvement in ROC [rate of climb]." The pilot reported having 12 hours of flight time operating out of airports above 3,000 feet mean sea level (msl) or above. Following the accident, the pilot underwent 5 hours of dual training at airports over 7,100 msl. The pilot also noted that he may have encountered windshear or turbulence as he retracted the gear during the attempted takeoff.
TESTS AND RESEARCH
The engine was examined and test-run on June 22, 2005, at Air Transport, Phoenix, Arizona with Safety Board investigator and FAA inspector present. The spark plugs were removed and the electrodes were black and sooty. The engine was manually rotated and thumb compression was obtained on all cylinders, in firing order. A borescope inspection revealed no mechanical deformation on the valves, cylinder walls, or on the internal cylinder heads. The engine was test-run and the magneto check produced a drop of 75 rpm on each magneto. No operational deficiencies were noted.
The Safety Board investigator completed weight and balance calculations for the accident flight. Based on weights given by the pilot and responding rescue personnel, the following information was determined:
Pilot and Passenger: 445 pounds
Rear Passenger: 210 pounds
Fuel: 372 pounds
Baggage: 45 pounds
Aircraft Weight: 1,695 pounds
Total Gross Weight: 2,767 pounds with a 44.85 center of gravity.
Using the airplane weight of 1,624 pounds, the following weight and balance calculations were determined by the Safety Board investigator:
Pilot and Passenger: 445 pounds
Rear Passenger: 210 pounds
Fuel: 372 pounds
Baggage: 45 pounds
Aircraft Weight: 1,624 pounds
Total Gross Weight: 2,696 pounds with a 44.9 center of gravity.
According to the POH for the airplane, the maximum takeoff weight is 2,650 pounds. Using the correct weight for the airplane, the accident flight was 117 pounds over the maximum gross weight. Using the airplane weight of 1,624 pounds, the airplane would have been 46 pounds over maximum gross weight.
Using performance data from the POH, the following information was noted and performance data calculated. With a maximum weight of 2,650 pounds, flaps up, cowl flaps open, and zero wind, the takeoff distance was calculated using a pressure altitude of 6,609 feet msl and temperature of 12 degrees Celsius. Interpolated calculations using the short field takeoff procedures outlined in Figure 5-4 of the POH, showed that the ground roll required was 3,118 feet (zero wind 3,464 feet) and the distance needed to clear a 50-foot obstacle was 3,741 feet (zero wind 4,157 feet). The chart indicated that in order to achieve the stated performance, the pilot must use the short field technique as specified in Section 4 of the POH. Figure 5-5, Maximum Rate of Climb, shows that the rate of climb would have been 327 feet per minute under the following conditions: flaps up; gear up; 2,700 rpm; full throttle; mixture leaned above 3,000 feet; cowl flaps open.
The POH further notes that prior to takeoff from fields above 3,000 feet elevation, the mixture should be leaned to give maximum power in a full throttle, static run-up.
Fueling records at the Grand Canyon Airport indicated that the airplane was topped off with fuel prior to departure.
A copy of the pilot's Complex Pilot Exam was obtained from Grey Eagle Aviation, Inc. The final series of questions involve a weight and balance calculation. The first question of the series states, "Is the aircraft within the envelope?" The pilot's answer was, "Within limits (if aircraft 1,624 pounds)."
According to the Airport Facility Directory Southwest (AFD/SW), runway 3/21 at the Grand Canyon Airport is 8,999 feet in length at an elevation of 6,609 feet msl.
Using a Safety Board computer program, the IIC calculated the density altitude to be 7,728 feet msl.
In the Pilot's Handbook of Aeronautical Knowledge (AC 61-23C) it states the following:
"Air density is perhaps the single most important factor affecting airplane performance. It has a direct bearing on the power output of the engine, efficiency of the propeller, and the left generated by the wings…when the air temperature increases, the density of the air decreases. Also, as altitude increased, the density of the air decreases. The density of the air can be described by referring to a corresponding altitude; therefore, the term used to describe air density is density altitude. To avoid confusion, remember that an increase in air density means a lower density altitude. Density altitude is determined by first finding pressure altitude, and then correcting this altitude for non-standard temperature variations. It is important to remember that as air density decreases (high density altitude), airplane performance decreases; and as air density increases (lower density altitude), airplane performance increases."