At 19:23 22 May 2020, Dave Springford wrote:
To expand upon Tim's note:

ENL = Engine Noise Level
MOP = Means of Propulsion

IGC does not allow ENL to be used for electric or Jet engines, they must
use MOP sensors.

ENL may be used for gas powered engines. This is not a new change for
the
IGC, but I think the OLC has just implemented the change in their
software.

Many FES owners have been using ENL for years, but it is my understanding
that this is no longer allowed by IGC as sufficient proof the FES was not
used.

Dave,

Can you point to a current reference for IGC only allowing MOP sensors for
FES please.

SC3C says:
11.2ENL figures –engine on
An ENL of over 700 is expected when the engine is running at climb power.
Over 900 is typical for a two-stroke engine, and over 700 for a
nose mounted 4-stroke. Values of 999 have been recorded with a
two-stroke engine runningat full power, and over 900 for a Forward Electric
System (FES) with the FR close behind it. These high ENLs are
produced for a significant time during a climb and can therefore be
attributed to engine running.

SC3B says:
1.4.2EngineRecordingSystems - General.
Enginerecording is by IGCENL and MOP systems that are designed to
differentiate between conditions of forward thrust from the engine system,
and gliding flight without the use of engine. The low frequency IGC
Environmental Noise Level (ENL) system uses a sensor inside the FR and is
most sensitive to acoustic noise between100and 200Hz. It was originally
designed to record the operation of two-strokepistonengines, but may also
record reasonable ENL numbers with Forward Electric Systems (FES) if the FR
is installed just behind the engine and its retractible propeller (subject
to testing to show this). Where the ENL system does not produce high
enough readings with certain types of engine an d FR installations, either
the FR location must be changed or an additional sensor under the MOP code
must be fitted so that three high MOP numbers are produced in each IGC file
fix line in addition to ENL. Difficult cases for Engine recording are in
1.4.2.2- 1.4.2.5 below, and more detailis in SC3Annex C (SC3C) Chapter 11,
and Chapter 5 of the FR Specification.

Which seems to be saying "Fit a MOP Sensor where ENL is not Satisfactory"
it does not seem to be mandating it in all cases.