Wdl 1B N317TW

Summary

On 11 September 1994 at about 15:11 local time, a Wdl 1B registered N317TW, operated by Airship Inernational, was involved in an accident near Farmingdale, New York, United States. 3 people were on board and nobody was injured. The aircraft was substantially damaged. The NTSB has published a probable cause for this accident; it is quoted in full below.

Date

11 September 1994 at 15:11

Classification

Accident

Location

Farmingdale, New York, United States

Coordinates

40.7304, -73.4403

Aircraft

Wdl 1B

Registration

N317TW

Category

Blimp

Engines

2

Operator

Airship Inernational

Operating rule

Part 91: General Aviation

Purpose of flight

Aerial Observation

Phase of flight

Not recorded

Route

Farmingdale → Unknown

Aircraft damage

Substantial

Weather

VMC

Light

Day

NTSB number

NYC94FA176

Nobody was injured.

INADEQUATE DESIGN OF THE AIRSHIP, WHICH ALLOWED THE CENTER BALLONET TO OVERFILL AND TO COLLAPSE THE TRUNKING TO THE FORE AND AFT BALLONETS, RENDERING THE AIRSHIP UNCONTROLLABLE. FACTORS RELATED TO THE ACCIDENT WERE: INADEQUATE MAINTENANCE BY THE COMPANY/OPERATOR, WHICH ALLOWED THE PURITY OF THE HELIUM TO DECREASE; AND THE CENTER DAMPER VALVE TO OPEN (OR TO BE LEFT OPEN FOR FLIGHT).

Quoted verbatim from the NTSB record. This site does not paraphrase or interpret it.

Read the full NTSB narrative

AFTER ABOUT 40 MINUTES OF FLIGHT, THE AIRSHIP CREW NOTED THE ENVELOPE PRESSURE BEGAN TO DROP. THEY TURNED BACK TO THE AIRPORT & DROPPED 300 LITERS OF WATER BALLAST 'PER THE FLIGHT MANUAL.' AT ABOUT 700'AGL & 2 MILES FROM THE AIRPORT, WITH THE PRESSURE LESS THAN 15MM, THE CREW REALIZED THEY WOULD NOT REACH THE AIRPORT. THE AIRSHIP WENT INTO A NOSE LOW ATTITUDE & WOULD NO LONGER MAINTAIN ALTITUDE. THE CREW SHUT DOWN THE ENGINES & ELECTRIC SYSTEM & LANDED IN A STREET, BUT THE GONDOLA & FORWARD PART OF THE ENVELOPE WERE DAMAGED. INVESTIGATION REVEALED THE CENTER DAMPER VALVE WAS OPEN. THERE WAS EVIDENCE THAT DURING FLIGHT, THE OPEN VALVE ALLOWED THE FORE & AFT BALLONETS TO EMPTY & THE CENTER BALLONET TO FILL. APPARENT, OVER-FILLING OF THE CENTER BALLONET RESULTED IN CRUSHING OF THE COLLAPSIBLE TUBE (TRUNKING) THAT WAS USED TO FILL THE FORE & AFT BALLONETS. THERE WAS EVIDENCE THAT AS THE AIRSHIP DESCENDED, THE TRUNKING REMAINED CRUSHED, THE ENVELOPE PRESSURE DROPPED, & THE FORE & AFT BALLONETS WOULD NOT CONTROL THE TRIM OF THE AIRSHIP. A POSTACCIDENT CHECK OF THE CENTER DAMPER VALVE REVEALED THAT IT WAS OPERABLE; THIS VALVE WAS FOR MAINTENANCE USE ONLY & SHOULD HAVE BEEN CLOSED FOR FLIGHT. THE CREW REPORTED HELIUM CONTAMINATION DURING SEVERAL DAYS PRECEDING THE ACCIDENT. PURIFICATION OF THE HELIUM HAD NOT BEEN ATTAINED & MORE HAD BEEN ADDED TO KEEP THE TOTAL AMOUNT HIGH, WHICH RESULTED IN LESS SPACE FOR THE FORE & AFT BALLONETS TO EXPAND.

Quoted verbatim from the NTSB record.