# NTSB CHI98LA342: MBB BK-117, N230H, Topeka, KS, August 28, 1998 - Type: NTSB accident investigation - Classification: Accident · No injuries · Limited investigation · Final report - Date: August 28, 1998, 10:53 local (15:53 UTC) - Place: Topeka, KS - Location: 38.9509° N, 95.6636° W: Placed by OpenAirDocs at TOPEKA RGNL (FOE), within about a mile (OpenAirDocs) - Nearby events: https://openairdocs.org/map.md?lat=38.9509&lon=-95.6636&mi=10 - Phase of flight: [Approach](https://openairdocs.org/ntsb-phases/500) (OpenAirDocs' grouping) - Highest injury: No injuries - Injuries: 3 uninjured - Status: Completed, report February 16, 2001 - Report: Approved by Office Director - Safety recommendations: Yes - ADs cited in the narratives: [AD 95-08-12](https://openairdocs.org/ad/95-08-12) (OpenAirDocs) - NTSB case key (mKey): 43801 - NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=CHI98LA342 - NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/43801/pdf - Page: https://openairdocs.org/ntsb/CHI98LA342 ## Probable cause the pilot's failure to assure the engine cowling was secured during the aircraft preflight which resulted in the cowling separating from the helicopter and damaging the main rotor and tail rotor system. Factors associated with the accident were the cowling not being secured and inadequate design of the latching system by the manufacturer. ## Sequence of events In NTSB's coding before 2008 (https://www.ntsb.gov/GILS/Documents/codman.pdf). - Airframe/component/system failure/malfunction, approach - cooling system,cowling - not secured (contributing factor) - aircraft preflight - inadequate, pilot in command (cause) - acft/equip,inadequate design, manufacturer (contributing factor) - cooling system,cowling - separation (cause) - rotor system - foreign object (cause) - Loss of control - in flight, approach - aircraft control - not possible, pilot in command - In flight collision with terrain/water, descent - uncontrolled - Roll over, landing - flare/touchdown ## Analysis The accident occurred on a maintenance test flight after having had the No. 1 engine replaced. When returning from the flight a 'severe bump' and 'loud bang' were experienced followed by the helicopter rotating to the right. A pilot landed the helicopter in a field during which time it rolled over on its left side. Post accident inspection revealed the No. 1 engine cowling separated from the helicopter inflight. This damaged the main rotor blades which resulted in an imbalance and subsequent loss of the tail rotor gear box. Both Hartwell cowling latches appeared in the closed position; however, the aft latch was not damaged as was the forward latch. The manufacturer is aware of similar problems and has issued service bulletins addressing the problems. The latest service bulletin, SB-MBB-BK 117-20-109, had not been incorporated on the accident helicopter. ## Factual narrative On August 28, 1998, at 1053 central daylight time, a Messerschmitt BK-117, N230H, operated by St. Louis Helicopters, dba Topeka Lifestar, collided with the terrain during a landing approach at the Topeka-Forbes Airport, Topeka, Kansas. The helicopter was returning from a maintenance test flight when a "loud bang" was heard and it began rotating to the right. The pilot was unable to control the helicopter and it descended to impact with the terrain. The helicopter was substantially damaged. The pilot and two mechanics on board were not injured. The local flight originated from the Topeka-Forbes Airport, at 1040 cdt. The pilot reported the purpose of the flight was to obtain engine matching adjustment measurements after having had a new No. 1 engine installed. The pilot reported that they felt a "severe bump like turbulence" when the helicopter was approximately 2 miles west of the airport. He reported that he and the mechanic in the front left seat, scanned the instruments and everything seemed normal. Within seconds there was "...a loud bang, yaw and the aircraft started to oscillate violently." Another mechanic who was in the back of the helicopter, facing rearward, informed the pilot that the tail rotor had departed the helicopter. The pilot reported the helicopter immediately began to rotate to the right. He reported that they were at an altitude of about 300 to 400 feet above the ground at this time and that he had already picked out a field in which to land. The pilot reported his main objective was to try and maintain as much control of the helicopter as possible, and to land in a level attitude. The helicopter touched down in an upright attitude then rolled onto its left side. Post accident inspection of the helicopter by Federal Aviation Administration Inspectors from the Wichita Flight Standards District Office and from the Rotorcraft Certification Directorate revealed the left engine cowling separated from the helicopter inflight. According to the FAA Inspectors the cowling separated from the helicopter which resulted in damage to the main rotor blades and the separation of the tail rotor gear box. Inspection of the cowling latches revealed the forward over center Hartwell latch was deformed and bent. The aft over center Hartwell latch was not damaged. All three wing head stud fasteners were missing. According to the inspectors the two forward wing head stud fastener holes were distorted/elongated. The wing head stud fastener hole on the aft portion of the cowling did not appear to be damaged. On June 26, 1989, MMB-Helicopters issued Service Bulletin ASB- MBB-BK 117-20-104, to "...ensure secure fit of main transmission cowling access door and engine cowling access door in the event of a hinge failure... ." This Service Bulletin addressed removing and modifying various latches of the transmission access doors and the engine cowling and the installation of new locks, the wing head stud fasteners. This service bulletin was made into Airworthiness Directive, AD 95-08-12. On June 16, 1997 Eurocopter issued Service Bulletin, SB-MBB-BK 117-20-109. This service bulletin calls for the installation of a hook system which will prevent the transmission and engine cowlings from fully opening if the fasteners on the cowlings are not correctly latched. This service bulletin was not incorporated on the accident helicopter. According to a technical representative from American Eurocopter, the service bulletins resulted from several occurrences where the engine and/or transmission cowlings inadvertently opened during flight. He stated that unless pressure is placed on the cowling when the Hartwell latch is closed, it is possible that it won't catch the bottom latch. In which case it appears as though the latch is secured when in fact it is not. He stated that due to the changes in airflow the cowlings have typically opened during the descents and not during cruise. The manufacturers BK-117 Flight Manual states that checking the security of the engine and transmission access doors is a preflight item which should be checked prior to every flight. ## Aircraft - Registration: [N230H](https://openairdocs.org/deregistered/N230H-1999-05-05), registration cancelled 1999-05-05, S/N 7136 (OpenAirDocs) - Reported make and model: MBB BK-117 - Registry model: [Messerschmitt-Bolkow-Blohm BK 117 A-4](https://openairdocs.org/model/messerschmitt-bolkow-blohm-bk-117-a-4) (registry code 5626017) (OpenAirDocs) - Category: Helicopter - Serial number: BK-117-A4 - Airframe hours: 3928 - Engines: Lycoming LTS-101-650B1 650 horsepower turbo shaft - Damage: Substantial damage - Flight: Part 91 - Operator: St. Louis Helicopters, doing business as Topeka Lifestar - Registered owner: Debis Financial Services - Airworthiness certificate: Standard, Normal - Last inspection: AAIP, August 13, 1998, 31 hours before - Departed: FOE - Airport: FOE, Forbes Field ## Flight crew As NTSB recorded them. NTSB leaves out names. - Pilot; age 58; commercial; airplane ratings: single-engine land; instrument ratings: helicopter; medical: class 2, valid medical--w/ waivers/lim; seat: right; flight hours: 6,401 total, 476 in this make and model, 5,563 as pilot in command, 65 in the last 90 days, 35 in the last 30 days ## Weather - Conditions: Visual (VMC), Day - Wind: 300° at 5 knots - Visibility: 10 statute miles - Lowest ceiling: none - Temperature: 79 °F, dew point 68 °F - Altimeter: 30.00 inHg - Observed at: FOE ## 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 19980828022359A](https://openairdocs.org/incident/19980828022359A), Aug 28, 1998: Bolkms BK117A4, Topeka, KS, Substantial damage. Helicopter was on a maintenance test flight when it crashed under unknown circumstances. Upon approach to (foe) tailrotor departed aircraft. Upon investigation… 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.