# NTSB FTW94LA055: Ebershoff Steen Skybolt, N360HP, Erie, CO, December 15, 1993

- Type: NTSB accident investigation
- Classification: Accident · No injuries · Limited investigation · Final report
- Date: December 15, 1993, 16:00 local (23:00 UTC)
- Place: Erie, CO
- Coordinates: 40.020713, -105.040779 (estimated)
- Nearby events: https://openairdocs.org/map.md?lat=40.0207&lon=-105.0408&mi=10
- Phase of flight: [Maneuvering](https://openairdocs.org/ntsb-phases/450) (OpenAirDocs' grouping)
- Highest injury: No injuries
- Injuries: 1 uninjured
- Status: Completed, report September 13, 1994
- Report: Approved by Office Director
- NTSB case key (mKey): 18981
- NTSB case page: https://web.ntsb.gov/investigations/?ntsbnumber=FTW94LA055
- NTSB report (PDF, downloads): https://data.ntsb.gov/carol-repgen/api/Aviation/ReportMain/GenerateNewestReport/18981/pdf
- Page: https://openairdocs.org/ntsb/FTW94LA055

## Probable cause

WAS FLUTTER OF THE FLIGHT CONTROLS.

## Sequence of events

In NTSB's coding before 2008 (https://www.ntsb.gov/GILS/Documents/codman.pdf).

- Airframe/component/system failure/malfunction, maneuvering
  - flight control surfaces/attachments - flutter (cause)

## Analysis

DURING A POST-MAINTENANCE TEST FLIGHT, THE PILOT ACCELERATED THE HIGHLY MODIFIED AEROBATIC AIRPLANE TO 190 MPH. IMMEDIATELY, THE FLIGHT CONTROLS BEGAN TO FLUTTER.  THE PILOT RAISED THE NOSE, SLOWED THE AIRPLANE, AND LANDED UNEVENTFULLY.  POST-ACCIDENT EXAMINATION REVEALED A FRACTURED LOWER RIGHT AFT WING SPAR, AND A LOWER LEFT AILERON ACTUATOR THAT HAD BUCKLED IN COMPRESSION OVERLOAD.

## Factual narrative

On December 15, 1993, approximately 1600 mountain standard time, N360HP, an Ebershoff Steen Skybolt, sustained substantial damage in flight near Erie, Colorado.  The pilot was not injured. Visual meteorological conditions prevailed for the test flight.

The following is based on the pilot/operator report and a subsequent interview.  Maintenance had recently been performed on the engine and the pilot was test flying the highly modified aerobatic airplane prior to it being returned to service.  He lowered the nose 45 degrees below the horizon and accelerated to 190 MPH.  Immediately, the flight controls began to flutter.  He reduced power, raised the nose, and slowed the airplane.  The pilot flew back to Jeffco Airport in Broomfield, Colorado, and landed uneventfully.  Post-accident examination revealed a fractured lower right aft wing spar, torn fabric on the lower left aileron, and a broken actuator.  According to a University of Denver metallurgist, the actuator "had buckled in compression overload."

## Aircraft

- Registration: N360HP (not matched to a registry record)
- Reported make and model: EBERSHOFF STEEN SKYBOLT (STEEN SKYB)
- Category: Airplane, amateur-built
- Serial number: DE1002
- Airframe hours: 1100
- Engines: LYCOMING IO-540-K1AS 350 horsepower reciprocating
- Damage: Substantial damage
- Flight: Part 91
- Registered owner: Ebershoff Airplane Co., Inc.
- Airworthiness certificate: Special, Experimental (Special)
- Last inspection: Annual, December 14, 1993, 1 hours before
- Departed: BJC, BROOMFIELD, CO

## Flight crew

As NTSB recorded them. NTSB leaves out names.

- Pilot; age 53; commercial, private; airplane ratings: single-engine land; medical: class 2, valid medical--w/ waivers/lim; seat: rear; flight hours: 2,500 total, 1,500 in this make and model, 2,500 as pilot in command, 25 in the last 90 days

## Weather

- Conditions: Visual (VMC), Day
- Wind: 180° at 4 knots
- Visibility: 50 statute miles
- Lowest ceiling: none
- Temperature: 50 °F

## 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 19931215047419A](https://openairdocs.org/incident/19931215047419A), Dec 15, 1993: Amtrsn SKYBOLT, Erie, CO, Substantial damage. Post maintenance test flight. Flight control flutter at 190MPH. Slowed and landed. Fractured spar. Aileron buckled.

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.

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