Ibra wrote:
CS23/CS25 certification G-limits could be misleading, you could argue that C210 may take up to 10G static without breaking while B777 up to 5G (there are documented cases on both airframes) but the two will break if speed control is lost under high G loads, however, airliners have very tight V-limits margins on their cruise altitudes
Yes on any aircraft when in marginal control due heavy turbulence or other reasons, speed control should be the top priority. If you have IAS indication, keeping wings level and IAS in the middle of the green go a long way towards surviving.
Airliners usually have auto-speed brakes and auto-idle-throttle when reaching Mmo/Vmo, and that helps with the much reduced speed margins they have in cruise.
I am sure the latest statement is wrong, even with altitude loss either ASI or VSI has to shoot over the roof on 80deg bank unless you are happy to take +3G or lose control at some point, you can’t “unload it forever”
Nobody mentioned “unloading forever”. When you have a chance, have a go at the 777 recovery procedure. It can be recovered from a 120 bank by unloading the aircraft to speed up roll rate, thrust idle and speedbrakes.
And finally remember that G-load is an acceleration, not a force. So 2G on a 777 imply significantly higher forces than 4 on a Cessna…
BeechBaby wrote:
Peter wrote:
Why did the engine stop?
Not sure. Co-Incidence? Really bad day at the office? I cannot get any info on why that happened. I thought they may lurk on EuroGa and could give us some insight but does not appear that way.
Good question. The engine air inlet is quite hail-proof as it is the big NACA duct you see on the RH side of the cowling in the picture, then a 90deg turn inboard into the air filter, then another 90 deg turn forwards into the turbocharger, so quite convoluted for hail to block, even less to get into the turbo. If the inlet is blocked by hail/ice, the louvres behind it, with zero protuberance into the airflow, are the alternate air, which spring-loads closed and opens when the main is blocked.
Even if some stones managed to get into the turbo and damaged it, the engine should still be capable of 45% power at FL140….not a lot, but it should increase to 75% during the subsequent descent.
Maybe the hailstone-damaged air filter or hailstones that went through it stopped the spring loaded alternate air valve from opening while blocking the main airflow…
Maybe some of the stones managed to damage some of the fuel injection system above the cylinders….
Either way I don’t think anyone designed this aircraft to fly in such wx…
T28 wrote:
So 2G on a 777 imply significantly higher forces than 4 on a Cessna…
Just as 1G does …but it is to be judged relative to its capability, rather than absolute forces, is it not?
Antonio wrote:
If you have IAS indication, keeping wings level and IAS in the middle of the green go a long way towards surviving.Airliners usually have auto-speed brakes and auto-idle-throttle when reaching Mmo/Vmo, and that helps with the much reduced speed margins they have in cruise.
Yes in theory if you keep the ASI in middle of green arc and keep wings level, high likely you won’t die !
But to go deep inside airframe flight enveloppe you will need to bring engine power near 30%-50%, you DO have this luxury in your piston engine but on airliners jet engines you DO NOT: you are not allowed to reach those low power points in engine flight enveloppe at high altitude cruise (on hand or auto throttle), you can’t idle it to recover from a dive or spin, the engines (at least CFM56 which I am familiar with) will flameout near 40% power at optimal cruise altitudes
So you can go for low power & slow speeds in airliners but,
- If you stall the engine, you have to wait for going down to lower altitudes 20kft-25kft before your engines can relight
- If you stall the airframe, you have to wait for thick air down to lower altitudes 8kft-12kft before you can recover
- If airframe cracks due to hail or stress, you are back to 10kft to breath
- If engine sensors get lot of hits, you are back to the ground
Of course, airliners can do very well dodging storms at 10kft given they have huge climbs & speeds to avoid but they are not robust for convective encounters at cruise altitudes, as start the pax are not strapped and are eating lunch !
Ibra wrote:
bellow 40% power near optimal cruise altitudes
That is 40% N1 which is much less than 40% available power in those conditions (and much much less than 40% TO rated power)
Ibra wrote:
It does not seem to me as “robust setup for loss of control in convective weather”
Do incident/accident statistics point to that lack of robustness?
Antonio wrote:
That is 40% N1 which is much less than 40% available power in those conditions (and much much less than 40% TO rated power)
You are right, just me being sloppy but at some low power threshold jet engines will not be able to turn on light air, especially, if they start idling while ingesting lot of rain, hail and snow, but when they run at 100%, they can crunch anything but one need to keep their wing level and speed in control for the airframe to keep up
https://en.wikipedia.org/wiki/Garuda_Indonesia_Flight_421
I am not sure what is the threshold on piston egines? but probably they also quit when you throw hail on them even at 100% power like in this C210 flight, who knows? but at least they don’t switch off completly with idle in light air when recovering from a loss of control, they just run out of steam 
Wiki from Garuda Flight 421 wrote:
pilots be advised to maintain a higher engine power level in moderate to severe precipitation to avoid flameout.
I was not aware of such advise or this accident, which supports your view. However, has this idle flameout been a widespread problem?
On most piston engines, rain or hail, and the P210 , in particular, due to engine air induction design, are very unlikely to stop the engine, although a power loss is to be expected. However, in this case, by the looks of the otherwise remarkably intact airframe, the stones that hit the leading edges were not of the ordinary 1/2" garden variety….
Airliners usually have auto-speed brakes and auto-idle-throttle when reaching Mmo/Vmo ….
Not on the B737!
There are some loss of control accidents where engines did shutdown during the upset recovery as it involved extreme idle regimes (recent one was Challenger that hit wake turbulence from A380 at cruise altitude, although I honestly would not expect any of GE & Safran engines to keep running or even stay attached when you are upside down with negative G-loaded wing)
The ones with idle on water/hail/ash/ice ingestion are very rare though but it’s something that the regulators have pointed to manufacturers as “action plan to remediate” during certification as ingestion tests by manufacturers are done on the ground not at cruise altitude but the main mitigation was that pilots “would not fly in extreme weather in cruise” still it did come up in few accident reports…
