ASN Wikibase Occurrence # 134852
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| Date: | Tuesday 26 July 2005 |
| Time: | 10:10 |
| Type: |  Bell 206L-3 LongRanger III |
| Owner/operator: | Illinois Department of Transportation |
| Registration: | N741LL |
| MSN: | 51165 |
| Year of manufacture: | 1986 |
| Total airframe hrs: | 8026 hours |
| Engine model: | Allison 250 C30P |
| Fatalities: | Fatalities: 0 / Occupants: 4 |
| Aircraft damage: | Destroyed |
| Category: | Accident |
| Location: | Justice, IL -
 United States of America
|
| Phase: | Manoeuvring (airshow, firefighting, ag.ops.) |
| Nature: | Unknown |
| Departure airport: | Downers Grove, IL |
| Investigating agency: | NTSB |
| Confidence Rating: |  Accident investigation report completed and information captured |
The helicopter was destroyed when it impacted a sign, a privacy/guard fence, and the terrain adjacent to an interstate highway. The public use flight was conducted in order to survey a tollway. According to the pilot, the helicopter began, "a sudden right yaw with possibly a raising of the tail. The aircraft then yawed left, possibly in response to pedal input ... Then started what seemed to be a slower right rotation." The helicopter continued to rotate to the right, descended, and impacted the structure of an overhead road sign, a privacy/guard fence and then came to rest on the ground adjacent to the fence. The reported winds in the vicinity of the accident site were 290 degrees at 15 knots. Radar track data showed that the helicopter traveled in a northwesterly direction parallel to an interstate highway, passed a toll plaza, and then began a left turn. The radar data showed that during the left turn, the wind direction relative to the aircraft ground track entered the region defined in the Federal Aviation Administration "Rotorcraft Flying Handbook" (FAA-H-8083-21), as being conducive to weathercock instability. During this same period, the helicopter's calibrated airspeed was between 4 and 20 knots. FAA-H-8083-21 states that, "In this region, the helicopter attempts to weathervane its nose into the relative wind. Unless a resisting pedal input is made, the helicopter starts a slow, uncommanded turn either to the right or left depending upon the wind direction. If the pilot allows a right yaw rate to develop and the tail of the helicopter moves into this region, the yaw rate can accelerate rapidly." FAA-H-8083-21 also states that, "Unanticipated yaw is the occurrence of an uncommanded yaw rate that does not subside of its own accord and, which, if not corrected, can result in the loss of helicopter control. This uncommanded yaw rate is referred to as loss of tail rotor effectiveness (LTE) and occurs to the right in helicopters with a counter-clockwise rotating main rotor." No anomalies were found with respect to the helicopter.
Probable Cause: The pilot's improper in-flight decision while maneuvering which resulted in a tailwind during low airspeed helicopter flight and subsequent loss of tail rotor effectiveness. The struck sign and fence were factors in the accident.
Accident investigation:
 |
|
Sources:
NTSB: https://www.ntsb.gov/_layouts/ntsb.aviation/brief.aspx?ev_id=20050805X01169&key=1
Location
Revision history:
| Date/time | Contributor | Updates |
|---|---|---|
| 21-Dec-2016 19:26 | ASN Update Bot | Updated [Time, Damage, Category, Investigating agency] |
| 06-Dec-2017 10:45 | ASN Update Bot | Updated [Operator, Other fatalities, Departure airport, Source, Narrative] |
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