Originally Posted by
FlightDetent
dated MAY 2016, extracted from the website.
Fifteenth Edition — 2007 AMDT 5
The mandatory read-back of units below 1000 mb seems to be a UK thing - I did rather thorough search of the ICAO paperwork.
I would consider it a constitucionalized best-practice against confusion with american operators used to inches, for reasons discussed and explained above. Anyone suffering from this UK requirement is actively participating on a safety net preventing trans-atlantic aircraft crashing into other traffic. Let's now make an informed decision how much to get aggravated
The rule was first implemented in CAP 413 edition 15 amendment 01 in December 2004, together with the "degrees" added after heading values ending in zero. Similar requirement exists for ATC personnel communicating over telephone, intercom of even relying company messages - readback and its verification included.
Today's wording (since JUL 2013 or older)
Like I said at #31, we're the only country that does it.
As for the 'degrees' thing, I adopted the TC 'best practice' of giving heading instructions as +5s ie 235, 185 etc during my last couple of years as an ATCO 'cos I was too lazy to keep saying degrees.