# NTSB CHI03LA217: Enstrom F-28C, N51699, Waverly, IA, July 20, 2003 - Type: NTSB accident investigation - Classification: Accident · No injuries · Limited investigation · Final report - Date: July 20, 2003, 08:30 local (13:30 UTC) - Place: Waverly, IA - Coordinates: 42.741943, -92.508056 - Nearby events: https://openairdocs.org/map.md?lat=42.7419&lon=-92.5081&mi=10 - Phase of flight: [Enroute](https://openairdocs.org/ntsb-phases/400) (OpenAirDocs' grouping) - Highest injury: No injuries - Injuries: 3 uninjured - Status: Completed, report June 30, 2004 - Report: Approved by Office Director - Parties: Federal Aviation Administration, Enstrom Helicopter Corporation - NTSB case key (mKey): 57556 - NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=CHI03LA217 - NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/57556/pdf - Page: https://openairdocs.org/ntsb/CHI03LA217 ## Probable cause The main rotor blade push-pull rods being corroded, sustaining fatigue, and separating in cruise and the main rotor blade contacting the tail boom during the emergency landing. Factors were the diminished aircraft control and the vibrations encountered during flight after the rod separation. ## Sequence of events In NTSB's coding before 2008 (https://www.ntsb.gov/GILS/Documents/codman.pdf). - Rotor failure/malfunction, cruise - condition(s)/step(s) not listed, manufacturer - rotor system,main rotor tension torsion bar - corroded (cause) - aircraft control - diminished (contributing factor) - rotor system,main rotor tension torsion bar - fatigue (cause) - rotor system,main rotor tension torsion bar - separation (cause) - rotor system,main rotor blade - vibration (contributing factor) - Forced landing, emergency landing - rotor system,main rotor - other (cause) ## Analysis The helicopter sustained substantial damage when the main rotor blade impacted the tail boom during a forced landing. The helicopter experienced in-flight vibrations prior to the forced landing. The pilot stated that the helicopter experienced extreme vibration in-flight at 200 feet above ground level. He said that helicopter control was "10% to nil." An examination revealed that one of three Push-Pull Rod Assemblies, part number 28-16253-1, was found corroded and separated. The operator's fleet of aircraft was examined and four other control rods were found with corrosion. Examination of the rod with the separation from the accident helicopter at the National Transportation Safety Board's Materials Laboratory revealed that "most of the fracture areas were on a plane that was nearly perpendicular to the longitudinal axis of the rod, indicative of a brittle fracture mechanism such as fatigue cracking." The pilot stated, "Pitch control rod has no inspection procedure at this time. It rusted from inside and not visible from outside." Subsequent to the accident, Enstrom issued Service Directive Bulletin (SDB) No. 0096. The bulletin directs visual inspection of control rods with part number 28-16253-1 and 28-16253-101 according to their time in service on F-28A, F-28C, F-28F, 280, 280C, 280F, and 280FX helicopters. ## Factual narrative On July 20, 2003, about 0830 central daylight time, an Enstrom F-28C helicopter, N51699, piloted by a commercial pilot, sustained substantial damage when the main rotor blade impacted the tail boom during a forced landing near Waverly, Iowa. The helicopter experienced in-flight vibrations prior to the forced landing. The sightseeing flight was operating under 14 CFR Part 91. Visual meteorological conditions prevailed at the time of the accident. No flight plan was on file. The pilot and two passengers were uninjured. The local flight originated from Waverly Municipal Airport, near Waverly, Iowa. The pilot stated: Flying with two passengers. Notice small [vibration] and about one minute later, extreme vibration 200 ft [above ground level] over trees and houses. [Initiated] emergency landing to parking lot. Vibration very extreme, if seat belts were not on it would have thrown occupants from aircraft. Control 10% to nil. Vibration was so bad that visibility was poor to none. Touchdown was not hard but #1 blade was flopping about and struck tail, damage to blade and tail cone. If we would have been over 200 [feet above ground level] this would have certainly been more serious. The Federal Aviation Administration and helicopter manufacturer performed an examination of the accident helicopter. The examination revealed that one of three Push-Pull Rod Assemblies, part number 28-16253-1, was found with a separation. The internal surface of that rod assembly was found corroded. Another rod assembly was disassembled and was found to contain a liquid. The helicopter's third rod assembly was disassembled. No anomalies were found with that third rod assembly. The operator's fleet of aircraft was examined and four other control rods were found with corrosion. The two rods from the accident helicopter were sent to the National Transportation Safety Board's Materials Laboratory for examination. The laboratory produced Materials Laboratory Factual Report number 03-085. Excerpts from the report stated: Visual examination of the fractured rod portion showed the presence of substantial rust-colored corrosion deposits on the inside of the rod adjacent to the fracture. These deposits extended over a distance of about 2 inches above the fracture location. The corrosion damage had thinned the wall of the rod adjacent to the fracture, and in some areas the corrosion appeared to penetrate nearly through the wall thickness to the exterior surface of the rod. ... Examination of the fracture areas on the larger portion of the broken rod after ultrasonic cleaning in acetone revealed that most of the fracture areas were on a plane that was nearly perpendicular to the longitudinal axis of the rod, indicative of a brittle fracture mechanism such as fatigue cracking. Concerning the pitch control push-pull rod assemblies, the pilot stated: Pitch control rod has no inspection procedure at this time. It rusted from inside and not visible from outside. Must remove both pitch control ends and visually check inside tube. Subsequent to the accident, Enstrom issued Service Directive Bulletin (SDB) No. 0096. The bulletin directs visual inspection of control rods with part number 28-16253-1 and 28-16253-101 according to their time in service on F-28A, F-28C, F-28F, 280, 280C, 280F, and 280FX helicopters. Excerpts from the bulletin compliance section stated: Within ten (10) hours time in service or at the next annual inspection, which ever occurs first, review the aircraft maintenance records to determine the date "new" main rotor push-pull rods were installed in the aircraft. If the installation date for "new" main rotor push-pull rods can not be determined from the maintenance records, use the aircraft "DATE MFD." found on the aircraft data plate. For main rotor push-pull rods (P/N 28-16253-1 or -101) in service for more than twenty (20) years, inspect the push-pull rods in accordance with (IAW) paragraph 5.1 of this SDB within ten (10) hours time in service or at the next annual inspection, which ever occurs first. For main rotor push-pull rods (P/N 28-16253-1 or -101) in service between ten (10) years and twenty (20) years, inspect the push-pull rods IAW with paragraph 5.1 of this SDB within fifty (50) hours time in service or at the next annual inspection, which ever occurs first. For main rotor push-pull rods (28-16253-1 or -101) in service less than ten (10) years, inspect the push-pull rods IAW paragraph 5.1 of this SDB before the push-pull rods reach ten (10) years time in service. ## Aircraft - Registration: [N51699](https://openairdocs.org/aircraft/N51699), registered now, S/N 416, built 1977 (OpenAirDocs) - Reported make and model: Enstrom F-28C - Registry model: [Enstrom F-28C](https://openairdocs.org/model/enstrom-f-28c) (registry code 3300407) (OpenAirDocs) - Registry engine: [Lycoming HIO-360 series](https://openairdocs.org/engine/lycoming-hio-360-series) (registry code 41524, reciprocating) (OpenAirDocs) - Category: Helicopter - Serial number: 416 - Airframe hours: 3100 - Engines: Lycoming HIO360E1AD 205 horsepower reciprocating - Damage: Substantial damage - Flight: Aerial observation, Part 91 - Registered owner: P and N Corp - Airworthiness certificate: Standard, Normal - Last inspection: Annual, July 6, 2003, 20 hours before - Departed: C25, WAVERLY, IA - Destination: C25 ## Flight crew As NTSB recorded them. NTSB leaves out names. - Pilot; age 60; injuries: none; flight instructor, commercial; airplane ratings: single-engine land, multi-engine land; instrument ratings: airplane; medical: class 3, valid medical--w/ waivers/lim; last flight review March 2, 2003; seat: left; flight hours: 45,000 total, 8,000 in this make and model, 45,000 as pilot in command, 200 in the last 90 days, 8 in the last 24 hours ## Weather - Conditions: Visual (VMC), Day - Wind: 290° at 7 knots - Visibility: 5 statute miles - Temperature: 75 °F, dew point 70 °F - Altimeter: 29.93 inHg - Observed at: ALO, 12 nm away ## 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 20030720036789A](https://openairdocs.org/incident/20030720036789A), Jul 20, 2003: Enstrm F28C, Waverly, IA, Substantial damage. (-23) As reported by the pilot, shortly after the accident. The helicopter took off from a Waverly parking lot, giving local area rides. At approx. 200' to… ## Other investigations on N51699 (1) 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. - [NTSB NYC88LA018](https://openairdocs.org/ntsb/NYC88LA018), Oct 25, 1987: Enstrom F-28C (N51699), Laconia, NH, substantial damage 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.