# NTSB MIA98TA215: Hughes TH-55A, N998MC, Savannah, GA, July 31, 1998 - Type: NTSB accident investigation - Classification: Accident · No injuries · Final report - Date: July 31, 1998, 09:30 local (13:30 UTC) - Place: Savannah, GA - Coordinates: 31.979848, -81.080734 (estimated) - Nearby events: https://openairdocs.org/map.md?lat=31.9798&lon=-81.0807&mi=10 - Phase of flight: [Maneuvering](https://openairdocs.org/ntsb-phases/450) (OpenAirDocs' grouping) - Highest injury: No injuries - Injuries: 1 uninjured - Status: Completed, report February 15, 2001 - Report: Approved by Office Director - NTSB case key (mKey): 43568 - NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=MIA98TA215 - NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/43568/pdf - Page: https://openairdocs.org/ntsb/MIA98TA215 ## Probable cause The loss of engine power for an undetermined reason, resulting in a forced landing, and an in-flight collision with a ditch. A factor in this accident was a high density altitude. ## Sequence of events In NTSB's coding before 2008 (https://www.ntsb.gov/GILS/Documents/codman.pdf). - Loss of engine power, maneuvering - aerial application - reason for occurrence undetermined (cause) - engine assembly,valve,exhaust - leak - Forced landing, emergency descent/landing - In flight collision with terrain/water, emergency descent/landing - terrain condition - ditch - rotor rpm - not maintained, pilot in command ## Analysis According to the pilot this was the second flight on that day. The first flight lasted 1.3 hours with 'no discrepancies noted.' The pilot said the second flight was 'normal' for the first 1/2 hour of flight. He completed five passes, and on the last pass at 40 feet above ground level [field elevation 25 feet msl], with right hand quartering headwind, he reported, '...an engine partial power loss.' He said the '...symptoms were main rotor started to droop below 490 RPM (2900 engine RPM).' He lowered the collective, rolled in full throttle, and raised the collective to stop the decent. He said the rotor RPM 'continued to droop.' The pilot tried to maneuver the helicopter past trees, and a mound of dirt to a flat area on the far side of a ditch. He could not maintain enough altitude or rotor RPM to clear the ditch, and contacted the far side of ditch with the left side of the helicopter. The pilot told investigators, that the helicopter was functioning properly before the accident, and he had no explanation for the loss of rotor RPM. An engine run revealed no discrepancies. A compression check, while the engine was hot, reveled low compression on cylinders No. 1 and 3. Both cylinders were removed, and both cylinders were found to have exhaust valves that were not seated completely. The calculated density altitude, based on a temperature of 31 degrees C (88F), altitude 65 feet msl, and an altimeter setting of 30.05 inches of mercury, all obtained from the Savannah 0953 weather observation, was 1868 feet. The pilot stated that the weight of the helicopter was '...1590 [pounds] at the time of the accident.' The maximum gross weight of the helicopter was 1670 pounds. ## Factual narrative On July 31, 1998, about 0930 eastern daylight time, a Hughes TH-55A helicopter, N998MC, operated by the Chatham County Mosquito Control Commission, crashed on Elba Island near Savannah, Georgia, while on a Title 14 CFR Part 91 public-use, aerial application flight. Visual meteorological conditions were reported and no flight plan was filed. The helicopter was destroyed. The commercial-rated pilot/mechanic was not injured. The flight originated from the Commission's heliport the same day, at 0900. According to the pilot, this was the second flight. The first flight had lasted 1.3 hours with "no discrepancies noted." The pilot said, "...the second flight was normal...for [the] first .5 of flight. I completed five passes...and on the last pass at 40 feet Agl [above ground level] with RH [right hand] quartering headwind, I had an engine partial power loss. The symptoms were main rotor started to droop below 490 RPM (2900 engine RPM). I lowered collective, rolled in full throttle, raised collective to stop decent. Rotor continued to droop." The pilot said, "...I tried to maneuver the helicopter past trees, [a] mound of dirt, to flat land on [the] far side of [a] ditch. I could not maintain enough altitude or rotor RPM to clear [the] ditch. I contacted far side of ditch with the unoccupied side [left] of [the] aircraft." The pilot told the NTSB investigator-in-charge and FAA Inspector, that the helicopter was functioning properly before the accident, and he had no explanation for the loss of rotor rpm. An engine run at idle rpm did not reveal any discrepancies. A compression check while the engine was hot revealed low compression on cylinders No. 1 and 3. Both cylinders were removed, and both cylinders were found to have exhaust valves that were not seated completely. The calculated density altitude, based on a temperature of 31 degrees C (88F), elevation 25 feet msl, altitude 65 feet msl, and an altimeter setting of 30.05 inches of mercury, all obtained from the Savannah 0953 weather observation, was 1,868 feet. The pilot stated that the weight of the helicopter was "...1590 [pounds] at the time of the accident." The maximum gross weight of the helicopter was 1,670 pounds. ## Aircraft - Registration: [N998MC](https://openairdocs.org/deregistered/N998MC-2013-08-21), registration cancelled 2013-08-21, S/N 66-18306 (OpenAirDocs) - Reported make and model: Hughes TH-55A - Registry model: [Hughes TH-55A](https://openairdocs.org/model/hughes-th-55a) (registry code 4471004) (OpenAirDocs) - Category: Helicopter - Serial number: 6618306 - Airframe hours: 5447 - Engines: Lycoming HIO-360-B1H 180 horsepower reciprocating - Damage: Destroyed - Flight: Public aircraft, Part 91 - Registered owner: Chatham Co. Commision - Airworthiness certificate: Special, Special flight (Special) - Last inspection: 100 hour, May 4, 1998, 29 hours before ## Flight crew As NTSB recorded them. NTSB leaves out names. - Pilot; age 40; commercial; airplane ratings: single-engine land; medical: class 2, valid medical--no waivers/lim.; seat: right; flight hours: 2,052 total, 1,050 in this make and model, 2,052 as pilot in command ## Weather - Conditions: Visual (VMC), Day - Wind: 270° at 7 knots - Visibility: 10 statute miles - Lowest ceiling: none - Temperature: 88 °F, dew point 73 °F - Altimeter: 30.00 inHg - Observed at: SAV ## FAA reports on this event (1) The FAA's own accident and incident reports, matched to the aircraft by N-number and date (OpenAirDocs). - [Accident 19980731028199A](https://openairdocs.org/incident/19980731028199A), Jul 31, 1998: Hughes TH55A, Elba Island, GA, Destroyed. (-23) Pilot for chatham county mosquito control commission (public aircraft), N998MC a TH-55A helicopter crashed after partial engine power loss. Engine power… From the NTSB's public API. Aircraft are matched to registry aircraft by N-number and event date, checked against the reported serial number, make and model; the registry's history has gaps, so older matches can be wrong. Compare the reported make and model. --- OpenAirDocs.org is an independent research project of [Contrail Labs](https://contraillabs.com/). It is not affiliated with the FAA or the NTSB. Source documents are U.S. government works in the public domain.