7th of July 2014, Torque gauge, Blog #711
- V2Aviation
- 1 hour ago
- 2 min read
An Air Tractor AT-502 was to operate an agricultural application (crop dusting) flight on this day in aviation history eleven years ago, on July 7, 2014. The flight was to depart Carthage (Illinois, USA) for a local mission. The aircraft was loaded with 364 gallons of agricultural chemicals, with both fuel tanks 3/4 full.
The weather was good, Visual Meteorological Conditions existed, with a light (5 knots) variable wind. The temperature was 31°C with the dewpoint at 19°C. The altimeter setting was 29.79 inHg. The private runway at Carthage was a grass runway, which was dry at the time of the aircraft's take-off run, which started at about 16.15 local time.
While taxiing to the end of the runway, the flaps were set to take-off position. After lining up with the runway center line the brakes were applied while the throttle was increased. With an engine torque of 1550 ft/lbs and the engine rpm above 2200, the brakes were released, and the aircraft commenced its take-off roll. In the first part (first 1/3) of the take-off, there were no problems. The pilot noticed that at the halfway point, the (expected) tail did not lift off the runway; this only occurred 2/3 down the runway. The pilot also noticed that acceleration was not as expected. However, this far into the take-off roll, the pilot was committed to the take-off. In an attempt to get airborne, the pilot dumped the load and attempted to fly the aircraft of the runway. This was successful and the aircraft cleared a pond at the end of the runway, however did not clear a bank at the far side of the pond as it didn't climb. The aircraft flipped on its back, coming to a sudden stop. The aircraft sustained substantial damage, and the pilot sustained minor injuries.
During an interview with the NTSB, which was investigating the accident, the pilot stated the engine did not lose power during the takeoff, and given the conditions of the day, it should have flown. A post-accident examination of the aircraft by a Federal Aviation Administration inspector revealed that the Pratt & Whitney PT6-27 engine had been replaced with a higher-powered -34 engine. On March 21, 2014, a new torque gauge was installed in the aircraft. The torque gauge installed was for the lower-powered -27 engine, which resulted in the redline on the gauge being lower than it should have been.
The NTSB concluded that the probable cause(s) of this accident were:
The airplane's inability to climb out of ground effect, which resulted from the pilot using a lower power setting than needed for take off due to the mechanic's installation of the wrong engine torque gauge.
The NTSB Aviation Investigation Final Report which served as the source for this blog can be accessed by clicking on the .pdf file below;