The Trident 3B variant had a RB162 booster engine fitted above the No.2 Spey. This added 15% thrust for 5% more weight and was only used during take-off and climb out when needed. See here:
Hawker Siddeley Trident - Wikipedia, the free encyclopedia
Last edited by Jhieminga; 1st Jun 2011 at 08:29.
Reason: Corrected the location of the RB162