Tom Knauff says the rare double release failure has occurred.
On your checkride, it is required -- sort of.

In the USA the "Double Release Failure" is included in the Private
Glider Pilot Practical Test Standards (PTS), Area of Operation IV,
Task G. It states that the applicant "Demonstrates simulated aero tow
abnormal occurrences as required by the examiner." Double release
failure is also referenced in the Commercial and Flight Instructor-
Glider PTS.

Some examiners in the USA require this demonstration. Others ask the
applicant to explain their actions (and signals).
Ask your CFIG and Examiner about this Task (and any other) in advance
in order to prepare for it.

Some important points.

The wake (prop wash / wing wash) of the towplane in descent will trail
behind almost level. The glider should be under this wake during the
descent.

Airbrakes should be kept unlocked and in hand, then deployed as
required for drag. The towrope must be kept tight.

The glider pilot should not be in a hurry to touchdown, but definitely
touch down just a bit before the towplane. Glider touch down while
the towplane is still higher than 1 meter may slow the towplane to
near stall.

Towpilots must understand the mission, particularly pattern shape,
power settings, descent rate and the options for go-around on tow.

I've done it many times at several sites after receiving excellent
instruction from Cindy at Caracole in California City many years ago.
Training is the key for all glider pilots and towpilots for this
maneuver.

Should we ask FAA to eliminate this requirement? NO, we don't need
the FAA digging into our PTS.

Do I require this maneuver at Marfa, Texas on your Practical Test
(checkride)?

Come visit! I'll show you a good time, and help you toward your
goals.

Burt Compton, Master CFI / FAA Designated Pilot Examiner
Marfa Gliders Soaring Center, southwest Texas
www.flygliders.com