GreatBear;
Fabulous post, thank you.
PTH:
DC ATE and CAPT AIRCLUES
You two are the only people on this thread worth reading.
Ouch!...
and given a choice between descending and getting my pitot tubes back and using more fuel or NOT getting my pitot tubes back and dying...what is wrong with this question.
I haven't left North America in my flying. But I have had to fly below the Flight Levels in jet transports for various reasons...the fuel penalty isn't that great...it is doable,manageable etc.
In setting aside the fuel penalty for flight at substantially lower altitudes with turbine-powered aircraft, which engine-type are you referring to, the PW1's or the high-bypass PWs or Trents? I don't know what the fuel flows are for the smaller engines but I think the differences would be among the factors affecting the decision-making process to descend. A descent to say, 10,000ft for "warmer" air could increase the burn such that one is burning into all contingency fuels and possibly the MFOB. It's a very big decision. Of course, (as DC-ATE points out), diversion fuel should be in the plan, and of course it is - in this case, a diversion, say, to Recife, in a serious emergency, would be a possible choice. Of course, we do not know what this crew faced.
That isn't to say a descent to clear ice buildup is unwise or questionable - the captain must do what s/he must do to ensure safety and survival, but as you would know, the decision is not a simple nor a straightforward one.
I tend to think that in the emergent circumstances faced by the AF cockpit crew, the time and therefore the availability of such a decision was perhaps not there. What do you think?
GEE GUYS (not dc8 and clues) ...what happens if you lose pressurization...and have to fly at 10,000feet!
Planning for these kinds of contingencies by overseas long-haul carriers is a matter of routine policy including pressurization loss and engine-out descents. - quick example, YVR - HNL, a plan involving a diversion at 10,000ft with engine ice ON would use SEA, PDX or SFO then HIL/OGG depending upon winds/temps.
Diversion routes from anywhere along the flight-planned route as well as at either the equal time points or equal fuel points are analyzed for potential icing at 10,000ft. Where indicated, fuel is added to handle the additional burn. In these cases, the emergency plan is to arrive at the diversion airport having burnt into the MFOB.
ClippedCub;
A classical spin entry into the water could explain a lot if the debris dispersion can be explained by wind and currents. Reviewing the 3-view, the rudder would be blanketed by the horizontal and with the wing sweep it would wind up pretty tight. The pitots wouldn't agree due to yaw rate and the rudder would be left in limited travel. Would be a tough recovery if it was even possible with the rudder limit. Would require a fluke (500 year?) warm air column with a sideslip at the stall break tough.
The notion that AF447 possibly entered a "flat spin" has been broached a few times.
I am not an engineer nor a mathematician so my question is informed by a bit of reading...always a dangerous thing! Please bear with me as I had never asked the question as to whether a transport category aircraft could "flat" spin:
Given some distance between the two points round which any aircraft, but in this case a jet transport, would be theoretically rotating in a spin, namely the forward point or center of gravity, (weight?) and the aft point, center of lift and given a normal CofG position (about 4k kg of fuel would be in the tail at that point), and intact vertical and horizontal stabilizers, could these two points produce a flat spin under specific circumstances?
I have always perhaps laboured under the understanding that a transport category aircraft in a fully-developed stall would produce a substantial nose-down pitch attitude, possibly with spiral characteristics if roll angles were high and which would take an enormous amount of sky from which to recover.
I realize that any mass can "spin" and any aircraft with a narrow CofG, CofLift relationship could be made to flat-spin, but the development of same given usual characteristics of a high-altitude full stall do not seem to me to be conducive to the development of a flat spin.
There is precious little in the literature. D.P.Davies covers it but there is no discussion about "flat" spins, just the spiral dive stability and of course the various stall conditions including the "super-stall".
The question is "out there" and has been asked, so I think it is important to understand the nature of the stall, the spiral dive and the propensity to spin (or not) of this kind of airframe/airfoil.
If the mods deem this "Tech Forum" stuff, so be it - see you there. I think however it is "in context".
Many thanks,
PJ2