B-52 Stratofortress after which the pilots made a successful landing. B-52 bombers instrumented for gust and manoeuvre loads recorded gusts from clear air turbulence considerably more than the design limit with highest loads at 34,000 feet. The English Electric Lightning T4 prototype fin failure was caused by inertial roll coupling while doing high-rate rolls. The fin was enlarged, strengthened and roll-rate limitations were imposed. However, the first T5 also had a fin failure while doing rapid rolling trials with rocket pack extended. A Lightning lost its fin due to interaction between aircraft in close proximity at low level when flying in formation at M 0.97, an aerobatic display routine. Limitations were imposed including separation between aircraft when in formation. Fin buffeting is a critical issue for fighter aircraft with twin or single fins because the fatigue life of the fin structure is reduced by the fluctuating loads caused by burst vortices impinging on the fin. The single fin on the Eurofighter Typhoon experiences buffet loads caused by burst vortices which originate from the canard and wing leading edges at high angles of attack. The sides of the top-mounted airbrake, when deflected, also shed vortices which impinge, after bursting, on the fin. Buffeting from the extended airbrake is highest when the airbrake effective angle of attack is greatest, which for a fully-extended airbrake is greatest at low aircraft angle of attack and least when manoeuvring. The McDonnell Douglas F/A-18 Hornet twin fins are subject to buffeting from the breakdown or bursting of the leading-edge extension (LEX) vortex in front of the tail. The addition of a LEX fence significantly reduces the buffeting and increases fin fatigue life. Configurations All-moving tail fin Aircraft with all-moving fins, but which did not enter service, were the North American F-107 and the BAC TSR-2 The Lockheed SR-71 Blackbird and North American X-15 used fixed stubs for the fins and rudders for the remaining height. Conventional rudders would have been inadequate for the SR-71 because excessive deflections would have been required for the engine-out case causing unacceptable trim drag. Early configurations put forward for the X-15 show a conventional fixed fin and trailing rudder, and a ventral fin. This was changed to dorsal and ventral fins each with the outer half acting as a rudder. Multiple tail fins Twin tail aircraft have two vertical stabilizers. Many modern combat aircraft use this configuration. The twin rudders may