N191TP

HISTORY OF FLIGHTOn September 19, 2013, about 1553 mountain daylight time, a Beech C90-A twin-turboprop airplane, N191TP, was substantially damaged when it impacted a field short of the runway at Idaho Falls Regional Airport (IDA), Idaho Falls, Idaho, during its final approach to the airport. The commercial pilot and one passenger received minor injuries, and one passenger received serious injuries. The airplane was owned and operated by WE FLY LLC of Idaho Falls. The business flight was conducted under the provisions of Title 14 Code of Federal Regulations Part 91. Visual meteorological conditions prevailed, and no Federal Aviation Administration (FAA) flight plan was filed for the flight.

According to the pilot, the airplane was based at IDA, and he and two passengers originated the day's flight sequence at IDA on the morning of the accident. The airplane was flown first to Pocatello Regional Airport (PIH), located about 45 nautical miles (nm) from IDA, where a third passenger boarded. The airplane then flew to Boise Air Terminal/Gowen Field (BOI), located about 165 nm from PIH, where the passengers deplaned to attend a meeting. About 5 hours after landing in BOI, the pilot and same passengers departed BOI for IDA, with an interim stop at PIH to drop off the one passenger. The flight from BOI to PIH was uneventful. The pilot and two remaining passengers reported that the flight from PIH to IDA was "bumpy" or "turbulent."

The pilot reported that when the airplane was on its final approach to runway 2 at IDA, a "master warning or caution" annunciator light illuminated, and the pilot was "pretty sure" that it was related to a fuel quantity/distribution issue. He stated that he then checked the fuel quantity gauges, and recalled that they indicated that the airplane still had fuel. He did not provide any elaborating information to the investigation regarding the fuel quantity or distribution in the airplane at the time of the event. The pilot did not recall anything else about the event, except that he "saw the ground coming up fast" and instructed his passengers to "hold on." One of the passengers recounted a similar version of the sequence of events. PERSONNEL INFORMATIONFAA records indicated that the pilot held a commercial pilot certificate with airplane single- and multi-engine land ratings, and an instrument-airplane rating. According to information provided by the pilot, he had approximately 3,975 total hours of flight experience, including about 2,500 hours in the accident airplane make and model. His most recent flight review was completed in June 2013, and his most recent FAA first-class medical certificate was also issued in June 2013. AIRCRAFT INFORMATIONFAA 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 and one nacelle tank per side (left and right). The usable fuel quantity for each main tank was 132 gallons, and the usable fuel quantity for each nacelle tank was 60 gallons, for a total usable fuel quantity of 384 gallons. In normal operation, fuel for each engine is supplied from its respective nacelle tank, and electrically-powered boost pumps automatically transfer fuel from each main tank to each respective nacelle tank. A cockpit-display annunciator light system indicates when fuel pressure in the transfer system drops to a pre-determined level, essentially indicating that the main tank no longer contains any usable fuel. The annunciator light bears the text "NO FUEL XFR."

The airplane was equipped with two fuel quantity indication gauges in the cockpit, one for each side of the airplane. A two-position switch was used to select the quantity displayed on the gauges; the switch positions would cycle the gauge display between either the amount of fuel in each of the nacelle tanks, or the total fuel (nacelle and main tanks) on each side of the airplane.

The airplane manufacturer's operating manual contained the following text in the Limitations section: "Do not take off if fuel quantity gages indicate in yellow arc or indicate less than 265 pounds in each wing system." This equates to a minimum takeoff fuel quantity of about 39.5 gallons per side. METEOROLOGICAL INFORMATIONThe 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. AIRPORT INFORMATIONFAA 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 and one nacelle tank per side (left and right). The usable fuel quantity for each main tank was 132 gallons, and the usable fuel quantity for each nacelle tank was 60 gallons, for a total usable fuel quantity of 384 gallons. In normal operation, fuel for each engine is supplied from its respective nacelle tank, and electrically-powered boost pumps automatically transfer fuel from each main tank to each respective nacelle tank. A cockpit-display annunciator light system indicates when fuel pressure in the transfer system drops to a pre-determined level, essentially indicating that the main tank no longer contains any usable fuel. The annunciator light bears the text "NO FUEL XFR."

The airplane was equipped with two fuel quantity indication gauges in the cockpit, one for each side of the airplane. A two-position switch was used to select the quantity displayed on the gauges; the switch positions would cycle the gauge display between either the amount of fuel in each of the nacelle tanks, or the total fuel (nacelle and main tanks) on each side of the airplane.

The airplane manufacturer's operating manual contained the following text in the Limitations section: "Do not take off if fuel quantity gages indicate in yellow arc or indicate less than 265 pounds in each wing system." This equates to a minimum takeoff fuel quantity of about 39.5 gallons per side. WRECKAGE AND IMPACT INFORMATIONThe 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. ADDITIONAL INFORMATIONAirplane 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 ...