Seems like we have a conundrum and the implausable situation of 2 engines being fuel starved at virtually the same time from some 'fluff' in the tanks (highly unlikely). Concluding with a 40min descent and held in a pattern over Lambourne for 5 minutes I can't see there was any ice either to bung them up. London was cold but not -57C.
I found the AAIB very interesting and thorough for the time allowed to them so far. Thank you.
The weather was mentioned from a METAR at Heathrow I believe at the time but didn't seem to mention anything abnormal when all reports for that day seemed to be anything but normal.
I would like to draw your attention to the METARs for the London area on that particular date here.
http://www.wunderground.com/history/...q_statename=NA
There are some very interesting Microburst/Windshear activity throughout the day in the London area from SSW with winds in excess of 50kts GUSTING to 75kts out of nowhere!! I also believe that the London Eye was closed at 13:00. Oh no!
Strong outflow from thunderstorms causes rapid changes in the three-dimensional wind velocity just above ground level. Initially, this outflow causes a headwind that increases airspeed, which normally causes a pilot/
(AUTOPILOT in this case) to reduce engine power if they are unaware of the wind shear.
This is where the engines have settled to just above idle. As the aircraft passes into the region of the downdraft, the localized headwind diminishes, reducing the aircraft's airspeed and increasing its sink rate. The pilot releases AUTOPILOT and demands more power, as passengers and witnesses on the ground 'heard the roar of the engines like a take off'.Then, when the aircraft passes through the other side of the downdraft, the headwind becomes a tailwind, reducing airspeed further, leaving the aircraft in a low-power, low-speed descent.
(Heres where you get your 108kts and on board passengers reporting sudden loss of height). 108kts is not the speed you want on any HEAVY Aircraft at anytime whilst in flight. This can lead to an accident if the aircraft is too low to effect a recovery before ground contact. As the result of the accidents in the 1970s and 1980s, in 1988 the U.S. Federal Aviation Administration mandated that all commercial aircraft have on-board windshear detection systems by 1993. Between 1964 and 1985, wind shear directly caused or contributed to 26 major civil transport aircraft accidents in the U.S. that led to 620 deaths and 200 injuries. Since 1995, the number of major civil aircraft accidents caused by wind shear has dropped to approximately one every ten years, due to the mandated on-board detection as well as the addition of Doppler weather radar units on the ground.
3 Greens and Happy Landings