THISL

AcronymDefinition
THISLThematic Indexing of Spoken Language
References in periodicals archive ?
So the right move would be to drop to 16,000 without waiting for THISL, but then remain at 16,000 even if you cross SPANE.
This means you remain at FL240 until Myton, fly FL210 from Myton to THISL, but then remain at 16,000 feet until given further instructions.