Since 2008 not a single ceiling light at LHR-T5 has been replaced (lights are 120ft off the ground) and it was getting very dark.
They tried to replace the bulbs using cherry-pickers and hydraulic lifts but “none were deemed to be practical or safe enough”.
Sooo they’ve called in specialists--- Wire Walkers
See article
Heathrow seeks high-wire walkers to change light bulbs - Telegraph

Makes you wonder how the bulbs were installed in the first place--stilt walkers?