Just suppose you are inbound to LHR in a B767 and the entirety of the UK and Western Europe is down to Cat 2 and 3 weather - it does happen - its happened to me.
A B767 on one engine is limited to Cat 1 weather - its not certified for SE autoland.
As you track past Frankfurt (Vis 150m cloud base 100' in blowing snow) one engine starts to act up - vibration indicators all over the shop, generally unstable engine parameters. You disconnect the AT and reduce the thrust lever on the suspect engine back to idle. The vibration goes away and the idle engine parameters stabilise at acceptable values.
If the Crew decide to shut the engine down -
because they have done 100s of assy approaches and landing in the sim - WTF are they going to land? Well they could fly 800nm back to Romania or Turkey, where the weather was Cat 1, 2 hours ago, on one engine, and hope it keeps running over all that awful weather, and the Alps.
Or they might decide, since the vibration and engine parameters were REALLY eye catching BEFORE they reduced thrust to idle, to declare a pan and divert into FRA and AUTOLAND because they can -
until they shut down that engine - which is still producing electricity and bleed air for anti icing.
Or they might decide since the exceedances were not extreme to continue on towards LHR, with that engine at reduced thrust, in the knowledge that they have a multitude of CAT 3b capable airports between them and LHR, about every 10-15 minutes in fact, where they can autoland if needed...provided they DON'T shut the engine down.
The minute you shut down an engine you MUST divert and land at 'the nearest suitable airport'. If, having reduced the engine to idle thrust,
its no longer misbehaving you DON'T...you have options...you could quite legitimately fly the 1 hr or so from abeam Frankfurt, past Cologne, Brussels and 10 other suitable airports, and land at your destination, LHR, and only THEN shut down the problem engine as you taxi in.
The VERY first serious question your Fleet C&Ting management and safety department will ask you, having shut down the engine and flown 800nm to a Cat 1 weather airport in Romania - probably by phone 'cause its gonna be about a week before they see you in person - is "What were the engine instrument readings after you, VERY properly, reduced thrust to idle?"
"Ahh...well...they were all in the green"
"Ok....well we will see you when you get back"
They then spend the next x days until you turn up at BS Castle for your tea and bikkies discussing amongst themselves why you are about the biggest moron mother nature ever breathed life into...and how many 10s of 1000s of $ your lack of judgement has cost the company.
The above scenario is just one where a crew, having looked at all options, could quite legitimately decide to not shut down a misbehaving engine until after they land.
Its what airline pilots are paid to do. Take into account ALL factors...including commercial factors...before making the safest/best decision.
Maybe the crew of the 737 in the thread starter's post looked at the NAV display and saw the 'nearest suitable' airport was Tamworth and said "Fck that...its running ok now at idle thrust...we go to BNE where the ground staff are, and the engineers, food, our own beds, the whores and beer are better - so we operate it on reduced thrust until it ****s itself OR BNE IS the nearest suitable, or we land"
Flawless logic and command judgment
