of the present invention permits the deletion of such external pipes and the associated hardware saving cost and weight further enclosing all major oil lubricated bearings within a single cavity permits the overall heat rejection to the oil to be reduced thereby lowering oil cooling requirements as mentioned this is due in part to the isolation of the bearings relative to the hottest section of the engine but also in part because the amount of hot secondary air flow blown into the cavity to create a pressure differential to seal the oil within the cavity is reduced due to the reduction in overall number of oil air interfaces particularly the main bearing cavity 60 preferably comprises only two main shaft seals about the low and high pressure shafts 36 38 a forward shaft seal 64 located just rearward or downstream of the boosted lp compressor rotor 26 and a rear shaft seal 66 located just forward or upstream of the hp compressor impeller 28 as the amount of secondary air flow into the oil cavity is reduced the amount of heat which is thus introduced the oil is accordingly reduced therefore the total amount of heat which much be removed from the oil is lower thereby reducing the size cost and weight of the oil cooling system required the main bearing cavity 60 also provides a single large volume of oil having a significant thermal mass thereby providing a more beneficial mass to surface area ratio than possible with several individual smaller cavities further decreasing the engine heat rejection to the oil another advantage of the large main oil cavity 60 is the elimination of the need for a separate agb oil scavenge system particularly with the present apparatus only gravity is required in normal operating attitudes to.