Large, slow-moving target. So much so that the RAF have decided that painting them white was not necessarily a good idea and have toned down their appearance somewhat.
The Spams have been painting their strategic transports grey since the late '80s, but there you go. Even a lick of paint doesn't disguise the fact that you're sitting inside an enormous RPG magnet - and no amount of CBA is going to save your arse if the kite gets zapped on finals.
The RAF hurriedly bought a couple of Tristars off British Airways immediately after the Falklands War when they realised it was rather a long way and the VC10s were getting quite knackered... and that was then!
Ironically, BA used their Tristars on the Middle Eastern run and the airframes had clocked up quite a few hours before BA decided to draw the Tristar fleet down. The RAF's first two ex-BA machines were some of the first to be sold off.
There was absolutely no way that a Tristar would get in to Stanley, so a new airfield at Mount Pleasant was built and the Tristar was the first kite to land there from the UK - aided in no small part by noteworthy ARRSEpedian Buck Felize.
Despite not having a hangar at Brize Norton big enough to house them, they bought a couple more off (the by then defunct) Pan-Am. Bear in mind that this was nearly twenty five years ago... and the airframes were pretty much fucked then.
Since those heady days, the RAF's fleet of Tristars has grown to nine - all operated by 216 Squadron, all 500 series models and all thirty years' old. Look on the bright side; at least you're not sat on a forty-year-old VC10.
So when your flight is delayed and the Mover tells you it's because the kite's fucked, he's not lying. It really is. The RAF is now the largest operator of the type, which in itself does not engender much in the way of confidence - especially as every other major operator has binned them.