http://www.ead.eurocontrol.int/pamsl...G_AD_2_EGLL_en
EGLL AD 2.20 LOCAL TRAFFIC REGULATIONS
(i) Reduced Engine Taxi(i) Pilots who intend to execute a Reduced Engine Taxi Out must report their intention to Heathrow Delivery on first
contact.
(ii) Reduced Engine Taxi can be used, at the discretion of the aircraft commander,
EXCEPT in the following
circumstances:
aa. By any aircraft that is required to cross an active runway;
bb. By any aircraft, from Terminal 4 (Z,W,T,V) when the southern runway is in use for landings;
cc. By any aircraft exiting T and turning west onto S due to jet blast affecting Stand 412;
dd. By B777 variants in G and H due to jet blast;
ee. Where commanders of aircraft are aware that their taxi routing or entry onto stand is likely to involve tight turns or
gradients requiring significant power increases.