Pilot Debrief

GEFA-FLUG GMBH AS-105-GD near Hartford, WI — 2017-06-15

Final reportCEN17FA231
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Date
2017-06-15
Location
Hartford, WI, USA
Airport
WN75
Aircraft
GEFA-FLUG GMBH AS-105-GD
Registration
G-SUNA
Category
BLIM
Highest injury
Serious
Fatalities
0
Phase of flight
Initial climb

Probable cause

The overpressurization failure of the airship envelope as a result of the airship's encounter with gusty wind conditions and thermal activity. Contributing to the accident was the jammed Plexiglass venting panel.

Contributing factors

Contributing to the accident was the jammed Plexiglass venting panel.

NTSB narrative

The commercial pilot stated that, before the 2nd aerial advertising flight of the day in the airship, he checked the wind conditions and determined that, although the wind was still within flight parameters, it would be increasing, which would make "flying more challenging." After 15 minutes of flight time, the pilot returned to land because the wind was stronger than forecasted. As the airship approached the runway the pilot released the drop line and attempted to open the Plexiglass panel that is used for venting and descent control. However, the panel jammed closed. Shortly thereafter, the airship encountered a thermal that caused the airship to rise. The airship leveled around 500 ft above ground level, at which time the pilot heard a "loud air explosion," which violently shook the airship. He looked up at the envelope and noted a panel of fabric located aft of his sitting position and near the top of the envelope was missing. Within seconds he heard up to four more air explosions. The pilot stated that the envelope began to sag, and the forward speed of the airship resulted in the nose of the airship collapsing in and around the burners, which ignited the fabric. The pilot shut off the fuel to the burners, secured his five-point harness, and braced for impact as the airship descended. After impact, the pilot was able to get out of the gondola and crawl a short distance before the ground crew arrived and pulled him away from the wreckage. The maximum wind for takeoff listed in the flight manual as 12 knots; the wind velocity reported 15 miles from the accident site at the time of the accident was 10 knots gusting to 15 knots; 1 hour earlier the wind velocity was 7 knots. The flight manual also stated that the airship must not be operated when thermals are present. Given the increase in wind velocity and the thermal activity, it is likely that a localized area of high pressure developed in the crown of the envelope that exceeded the strength capability of the envelope, resulting an overpressurization and the subsequent explosive failure of the balloon fabric. It is also likely that the jammed Plexiglass panel used for venting prevented the pilot from relieving pressure in the envelope as the airship climbed.

Analysis

Primary failure mode
Mechanical failure
First missed decision gate
Pilot could have aborted the flight due to unfavorable wind conditions.

NTSB coding

Evidence available

  • Photos
  • 14 docket documents
View NTSB final reportView NTSB docket

Docket documents14

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