WPR13LA416

The pilot's inadequate preflight fuel planning, which resulted in departure with insufficient fuel to complete the flight, and consequent inflight power loss due to fuel exhaustion.

The airplane was equipped with two main fuel tanks (132 usable gallons each) and two nacelle fuel tanks (60 usable gallons each). In normal operation, fuel from each nacelle tank is supplied to its respective engine, and fuel is automatically transferred from each main tank to its respective nacelle tank. While at the airplane's home airport, the pilot noted that the cockpit fuel quantity gauges indicated that the nacelle tanks were full, and he believed that the main tanks had fuel sufficient for 30 minutes of flight. The pilot did not verify by any other means the actual fuel quantity in any of the tanks. Thirty gallons of fuel were added to each main tank; they were not topped off. The airplane, with two passengers, then flew to an interim stop about 45 miles away, where a third passenger boarded. The airplane then flew to its destination, another 165 miles away. The pilot reported that, at the destination airport, he noted that the cockpit fuel quantity gauges indicated that the nacelle tanks were full; he surmised that the main fuel tanks were not empty but did not note the actual quantity of fuel. Forty gallons of fuel were added to each main tank. Again, the main tanks were not topped off, and the pilot did not verify by any other means the actual fuel quantity in any of the tanks. The return flight to the interim stop was uneventful. The third passenger deplaned there, and the airplane departed for its home airport. While on final approach to the home airport, both engines stopped developing power, and the pilot conducted a forced landing to a field about 1.2 miles short of the runway. The pilot later reported that, at the time of the power loss, the fuel quantity gauges indicated that there was still fuel remaining in the airplane.  Postaccident examination of the airplane revealed that all four fuel tanks were devoid of fuel. The examination did not reveal any preimpact mechanical anomalies, including fuel leaks, that would have precluded continued flight. The airplane manufacturer conducted fuel-consumption calculations for each of the two city pairs. Because the pilot did not provide any information regarding flight routes, altitudes, speeds, or times for any of the flight segments, the manufacturer's calculations were based on direct routing in zero-wind conditions, nominal airplane and engine performance, and assumed cruise altitudes and speeds. Although the results are valid for these input parameters, variations in any of the input parameters can significantly affect the calculated fuel requirements. As a result, although the manufacturer's calculations indicated that the round trip would have burned less fuel than the total available fuel quantity that was derived from the pilot-provided information, the lack of any definitive information regarding the actual flight parameters limited the utility of the calculated value and the comparison. The manufacturer's calculations indicated that the accident flight leg (from the interim airport to the home airport) would have consumed about 28.5 gallons total. Given that the airplane was devoid of fuel at the accident site, the pilot likely departed the interim airport with significantly less than the manufacturer's minimum allowable departure fuel quantity of about 39.5 gallons per side. The lack of any observed preimpact mechanical problems with the airplane, combined with the lack of objective or independently substantiated fuel quantity information, indicates that the airplane's fuel exhaustion was due to the pilot's inadequate and improper pre- and inflight fuel planning and procedures.

The airport was equipped with an air traffic control tower (ATCT), which was staffed and operating at the time of the accident. According to information provided by the FAA, the pilot first contacted IDA ATCT when the airplane was about 18 miles southwest of IDA; the pilot advised that he was operating under visual flight rules, and that he was inbound for landing with the appropriate airport arrival information. The controller asked the pilot whether he was "better set up" for left or right traffic for runway 20. The pilot responded that although he was better set up for right traffic for runway 20, he preferred runway 2. The controller advised the pilot of another arriving aircraft, and instructed the pilot to report when he was 5 miles south of the airport, which the pilot acknowledged. After the other airplane landed, the controller queried the pilot of N191TP as to his current location. The pilot responded that he was 8 miles south of IDA. The controller cleared the pilot for a straight-in approach to, and landing on, runway 2, which the pilot acknowledged. However, the pilot then requested confirmation of the instructions. The controller advised the pilot that the airplane was in sight, and again cleared the pilot to land on runway 2. When the airplane was on about a 2-mile final, the controller advised the pilot to check that the landing gear was extended, which was a common practice at the IDA ATCT. The pilot did not acknowledge that transmission, or a subsequent one. The controller then observed the airplane yaw airplane-right, and descend to the ground, more than a mile short of the runway. The controller then alerted "crash fire rescue" via the "airport crash phone." According to FAA information, IDA was at an elevation of 4,744 feet above mean sea level. It was equipped with two paved runways, designated 2/20 and 17/35. Runway 2/20 measured 9,002 feet by 150 feet, and runway 17/35 measured 4,051 feet by 75 feet. Airplane Fuel Loading According to the pilot, prior to beginning the flight from IDA, he determined that the nacelle tanks were full, and that he then had 30 gallons added to each main tank. He did not visually determine the fuel quantities in any tanks; he based his determination of the nacelle tank fuel quantities on the fuel gauge indications. The pilot reported that after landing at BOI, he again determined that the nacelle tanks were full, and that the main tanks were not empty. He based those determinations respectively on the fuel gauge indications, and the fact that the "NO FUEL XFER" annunciation light had not illuminated during the flight from PIH to BOI. The pilot then had 40 gallons added to each main tank while at BOI. Although requested by the investigation, the pilot did not specifically report how much fuel was in each main tank, either before or after the addition of the fuel at IDA and BOI. The pilot's only statement regarding the fuel quantity in the main tanks was that "the wing tanks had about 30 minutes worth of fuel" prior to the initial upload at IDA, but he did not provide the basis for that assertion. The pilot stated that the airplane fuel consumption "averages" 70 gallons per hour. The pilot did not provide any information regarding the onboard fuel quantity for the takeoff from PIH on the accident leg of the return trip. Airplane Manufacturer's Fuel Consumption Estimate In response to an NTSB request, the airplane manufacturer provided the estimated fuel consumption quantities for the two city pairs. The calculations assumed direct flights between the airports, a cruise altitude of 8,000 feet for the segment between IDA andPIH, and 12,000 feet for the segment between PIH and BOI. Those altitudes were suggested by the manufacturer as normal altitudes for the segment lengths. The calculations were predicated on direct routing, zero-wind, and nominal airplane and engine performance at normal cruise speeds. Based on those conditions, the IDA-PIH segment would have consumed about 28.5 gallons, and the PIH-BOI segment would have consumed about 68.5 gallons. The calculated total fuel burn for the full round trip flight sequence was 194 gallons. The manufacturer calculated that the segment between IDA and PIH would have taken 0.22 hours (about 13 minutes), and that the segment between PIH and BOI would have taken 0.74 hours (about 44 minutes). The calculations yielded a total one-way trip time of 0.96 hours (about 58 minutes), but did not did not include start-up or taxi allowances. The manufacturer indicated that a visual flight rules fuel reserve of 30 minutes would have required about 46 gallons, which would result in a total trip fuel quantity requirement of 240 gallons. Manufacturer's data indicated that for altitudes 12,000 feet and below, fuel consumption rates ranged between about 92 and 102 gallons per hour in cruise, and between about 104 and 120 gallons per hour in climb. Fuel Consumption Quantity Reconciliation No records regarding the actual flight times, routes, altitudes, speeds, or fuel quantities were provided for the investigation. Calculations based on the pilot's statement that, prior to the first flight of the day, the main tanks contained about 30 minutes' worth of fuel, and his stated fuel consumption rate of 70 gallons per hour, yielded a pre-fueling main tank quantity estimate of about 35 gallons total. Calculations based on the pilot's reported information of the initial main tank quantity (35 gallons), full nacelle tanks (120 gallons), and the two fuel uploads (140 gallons), indicated that a derived fuel quantity of 295 gallons was available for the overall round trip. That value was 55 gallons more than the airplane manufacturer's calculated required quantity (including reserves), and 101 gallons more than the manufacturer's estimated required quantity, excluding reserves. The investigation derived an available fuel quantity for the return trip that was based on presumed near-empty main tanks (for conservatism), the pilot's report of full nacelle tanks, and the upload of 80 gallons. Based on those conditions, the calculated pre-departure minimum available fuel quantity for the return trip would have been 200 gallons. The IDA 1553 automated weather observation included wind from 210 degrees at 3 knots, visibility 10 miles, clear skies, temperature 17 degrees C, dew point 0 degrees C, and an altimeter setting of 30.19 inches of mercury. The airplane impacted a level plowed field about 1.2 miles short of runway 2, struck an irrigation ditch and berm approximately perpendicular to the direction of travel, and came to rest about 60 feet beyond the ditch. The initial ground scars were located about 150 feet prior to the final resting point, and the ground scars and the airplane longitudinal axis were oriented approximately towards the runway. The airplane remained upright, and the landing gear and left propeller were separated from the airplane. The right engine was partially separated from the right wing, and the aft fuselage was buckled and torn. Landing gear damage was consistent with the gear being extended/down at the time of impact. One nacelle tank was breached, but the other three fuel tanks were intact. The filler neck caps on all four tanks remained securely installed. The on-scene inspector stated that there was "no fuel observed" in either of the main tanks, and noted that the nacelle tanks "were both empty." The recovery personnel obtained a total of about 1/2 gallon of fuel from the airplane, and stated that there were no indications that "any significant" amount of fuel had leaked from the breached nacelle tank. There were no indications of pre- or post-impact fire. FAA information indicated that the airplane was manufactured in 1989, and was equipped with two Pratt & Whitney Canada PT6A turboshaft engines. Airplane manufacturer's information indicated that the airplane was equipped with one wing (main) fuel tank a