A read to take your mind off the markets, michael, malcom or whatever ....
Coffin Corner revisited.
In connection with the Air France Airbus disaster, the old aeronautical term “Coffin Corner” has been revived. This phenomenon was first encountered 55 years ago when the Boeing Stratojet (B47) entered USAAF service. A revolutionary six engined jet bomber, using swept wings developed from German research, the B47 flew at high altitude & mach numbers, conditions where it could enter “Coffin corner" At high altitude there is an altitude where limit speeds converge - stall speed and mach buffet speed. Just below that altitude is coffin corner, in which the operating margin between the limit speeds is very small.
B47 cruise at high weights had the aircraft flying in a critical margin of 10 knots or so between low speed stall and high speed buffet; but as fuel was burned off so the margin increased. In actuality, few B47 aircraft if any were lost were lost due to ‘Jet Upset’, strict operating procedures using the autopilot kept the aircraft in the safe margin.
Today's second-generation jet aircraft (B747-400 & Airbus A330) typically cruise at a constant mach number of 0.85 to 0.87. The actual altitude varies depending on the aircraft and atmospheric conditions. The doomed Air France Airbus A330-200 was apparently flying close to its maximum altitude; it then encountered large and severe thunderstorm activity, causing extreme variations in altitude. Normally with fully operational Air Data and Flight Management systems, the aircraft remains under control; after all this happens every day whenever an airliner transits safely through the Inter Tropical Convergence between north & south hemispheres.
However, its been theorized that this Airbus A330’s Air Data system was sensing airspeed incorrectly, in combination with very severe turbulence - possibly bringing the aircraft into Coffin Corner, so encountering limit speeds, which then caused an upset beyond pilot control.
Interestingly enough and not directly connected with the Airbus problem, a proposed new US Federal Aviation Administration flight training rule is designed to help pilots better prepare for rare but often fatal, upset flight conditions, The rule is set to open a broad debate on how best to enhance the growing ranks of civilian simulators to reduce loss-of-control (LOC) accidents. The FAA, as part of its new rule, wants pilots to regularly experience "in-flight manoeuvres in upset and disturbance recovery" in simulators, scenarios often covered in ground school but not in a simulated environment.
------------------------------ Low speed limit: - At high altitude air density and lift, decreases. Therefore stall speed increases. (Simply – Low speed stall) High speed limit: - At high altitude, mach speed decrease. Therefore mach buffet speed decreases. (Simply – High speed stall) =========================
