P47, think you have several valid answers to choose from , Here may be a few more thoughts .
Modern a/c generally have much better payload/range than older types , so the need for exploring the edges of the fuel rule book is much reduced .
Some of the techniques used are ...
HKG non stop LHR in the early days , and even SIN-LHR in a recent 744s , can be payload limited in strong headwinds .
Some pax and freight would be Weight [ not wait ] limited . Thus on the day with light winds they could be got on , other days freight and standby pax would be offloaded to enable enough fuel wt to be loaded for a non-stop service .
Another technique is to replan in flight ... 25yr old Tristar -100 with 393 pax Bahrain - Gatwick , winter , thus strong headwinds . we'd leave perhaps 5000kgs of fuel short of flight plan . ATC flight plan stayed to LGW , our fuel plan to Cyprus -div Athens .. Climb well and get a short cut , optimum level , best range speed , burn contigency in flight . Shame the opposite direction RAF Tristar had to dump fuel to get to landing wt ! If we'd had a probe we could have had it . Approaching Athens fuel looked good to plan to Brussels -div LGW . Approaching BRU and top of descent , fuel looked good to plan LGW -div Bournemouth . Landed above legal limits , had to be good weather , and no holding delays.
If we'd not been able to save enough fuel for the above , then it would be a Gas 'n Go for a top up somewhere along the route .
Approach swops ... holding at LHR , if really short get on company frequency , ask them to arrange an approach swop with another co. a/c with more fuel ...
Mind you early days of A320s at LHR , someone ups and says '' in 10 mins we need to divert '' ..... ''Where '' says ATC . ''27R from 27L'' say a/c
''.....'' ! says ATC ... 2 more a/c pipe up with same info .. A320 management had to back off fuel savings a bit .
Island Reserve was another tool in the fuel tool box . Something like LHR-Bermuda in the old days , nearest div. is New York JFK [ 700nm ]nto wind . 707s could not do that , so at the PNA [ point of no alternate ] decision was made to go on or div. If to go on , weather had to be good , airfield open , etc. and 2 hours holding fuel at BDA had to be onboard.
2 hours should have been enough to bulldoze any smoking wreck of the runway reserved for you .
rgds condor .