PA-25 pilot reported the aircraft lost power at 100 ft AGL when the fuel vent line became clogged.

Attributes
ACN	1456951
Time
Date	201705
Local Time Of Day	0001-0600
Place
Locale Reference	ZZZ.Airport
State Reference	US
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Make Model Name	PA-25 Pawnee
Operating Under FAR Part	Part 91
Flight Phase	Takeoff
Route In Use	Visual Approach
Flight Plan	None
Component
Aircraft Component	Fuel Line Fittings & Connectors
Person 1
Function	Pilot Flying Single Pilot
Qualification	Flight Crew Instrument Flight Crew Private
Experience	Flight Crew Last 90 Days 1 Flight Crew Total 540 Flight Crew Type 30
Events
Anomaly	Aircraft Equipment Problem Critical Inflight Event / Encounter Fuel Issue

Narrative:

The piper pawnee PA-25-235 was being used as a tow plane in glider operations. A schweitzer 2-33 glider was in tow when the tow plane lost power approximately 100 feet off the ground. The glider was released and both the tow plane and glider landed on the far end of the runway with no damage. This particular PA-25-235 has been modified for towing operations with a hopper fuel tank. Upon stopping the plane and further investigation; I noted 85%+ fuel in the plane. When I opened the fuel tank cap; the fuel tank popped up/out approximately 1'. After further investigation; the fuel vent line was completely plugged and had caused a complete vacuum in the fuel system. I have no knowledge of a proper vent cover on this pawnee and it has been flying for years from what I can tell with no vent tube cover. I hope by filing this report that other owners of PA-25-235 with modified hopper fuel tanks ensure that they are using fuel vent tube covers. This was the 5th flight of the day in this plane and this is a particularly difficult if not impossible item to pre-flight.

Original NASA ASRS Text

Title: PA-25 pilot reported the aircraft lost power at 100 FT AGL when the fuel vent line became clogged.

Narrative: The Piper Pawnee PA-25-235 was being used as a tow plane in glider operations. A Schweitzer 2-33 glider was in tow when the tow plane lost power approximately 100 feet off the ground. The glider was released and both the tow plane and glider landed on the far end of the runway with no damage. This particular PA-25-235 has been modified for towing operations with a hopper fuel tank. Upon stopping the plane and further investigation; I noted 85%+ fuel in the plane. When I opened the fuel tank cap; the fuel tank popped up/out approximately 1'. After further investigation; the fuel vent line was completely plugged and had caused a complete vacuum in the fuel system. I have no knowledge of a proper vent cover on this Pawnee and it has been flying for years from what I can tell with no vent tube cover. I hope by filing this report that other owners of PA-25-235 with modified hopper fuel tanks ensure that they are using fuel vent tube covers. This was the 5th flight of the day in this plane and this is a particularly difficult if not impossible item to pre-flight.

Data retrieved from NASA's ASRS site and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.