CJ, can you give us more detail about this incident? This is the first FES failure I've heard of. You said the FES had to be shut down at "moderately low" altitude, which suggests it didn't run for very long. It's surprising that it could overheat so quickly. How long did the FES run before the shutdown? What was the OAT at the time? What altitude MSL did it fail at? Was the battery damaged? Was there any smoke or burning smell? Has the manufacturer or owner inspected the FES system since the incident?

Hi Ben,
I wouldn't classify it as a 'failure' as the system worked as advertised. Like any other sustainer (jet, internal combustion, etc) a FES has capacity and operating temperature limitations. These were reached and in accordance with system warnings, the pilot shutdown to prevent damage. To answer your questions (to the best of my knowledge):
- Duration: It had been run previously, hence low capacity and high temp
- Duration immediately before incident: Unknown
- OAT: 86F (approx)
- ALT: Unknown (suspect 2,500AMSL, approx)
- Damage: Nil, it was shutdown in accordance with system warnings. No smoke/smell reported.
- Inspection: Yes. Owner and maintenance provider.

The de-identified summary of the incident is publicly available so I can reproduce it below:

"RUNWAY EXCURSION LAK-19

The pilot was flying cross-country on a weak day and decided to return to the home airfield using the electric sustainer motor. The pilot subsequently flew through lift and decided to continue on task. On return from the turn point the pilot found himself getting low again, so he restarted the electric motor and headed towards some hills in search of lift. Unfortunately, the battery power was low and the motor warning lamp illuminated. The pilot turned off the motor and was immediately faced with an outlanding. While the aircraft was now over hilly terrain with limited landing options, the pilot located a paddock of suitable dimensions with some minor slope. The glider landed at speed and it is suspected that the wheel and starboard wingtip touched the surface simultaneously, resulting in the wing catching in long Lucerne and causing the glider to ground loop. The aircraft was substantially damaged - suffering a bent undercarriage and separation of the starboard wing extension. Pilots of gliders capable of self-retrieving need to fully understand the limitations of their type of motor and must make decisions at sufficient height and with safe landing options available."

Please don't misunderstand the intentions of my post. I'm a fan of the FES in theory and in practice. Personally, I think the next jump in battery technology will push it over the top. It's just that discussions on this topic often include comments on the 'infallibility' of the system. My post was intended to give a real world example of why we still need to apply basic gliding principles to this propulsion type, just like the rest of them.

CJ