There is a delightfully coloured
pink AIC issued by those clever chaps at AIS that discusses instrument pressure settings in conditions of abnormally low atmospheric pressure settings.
When these conditions prevail, perceived wisdom is, unless you have an altimeter suitably adorned with a setting range that accommodates a QNH below 950 and IMC is likely to be encountered, which is prob 90, given the instability in the atmosphere at these barometric levels – take off should not be made.
If VMC prevail for the whole flight – set system to lowest possible setting and chug along with alacrity.
Instrument let downs in UK on QNE, in IMC because the altimeters can’t read the correct QNH might at best induce a cosy chat with insurers over tea and biscuits. At worst – a more profound meeting with those cheerful chaps at the Coroner’s Court who constantly complain about unnecessary workload.
