High speed below FL100, why or why not?

[AV8R-77]

Hello all,

What are your opinions with regards to (planning) a high speed descend profile, including high speed below FL100, ie. 330kts till 3000ft? And as well high speed climb, (accelerating at 5000ft or below)....

What are the pro's and con's? I can think of a few myself but i'm curious to what others think. What does your SOP say?

Any documented facts with regards to time saving, fuel economy, airframe stress, bird strike risk etc? Personally I don't like high speed below FL100, during descend nor climb.
Regards,
AV8R

[richarjm]

For me the biggest consideration is VFR traffic. If there is an excellent radar service then high speed is less of a risk, especially in class A,B and C airspace. If there are generally high levels of VFR traffic where you operate below FL100 it's just not worth the risk, time/fuel savings be dammed.
See also
http://www.pprune.org/forums/showthr...hreadid=125808

[Fatter Bastard]

um, you get there quicker . F#ck it - I am not paying for the gas!

[eyeinthesky]

Aren't some windscreens only certified for bird strike tolerance up to a certain IAS? (BA146 for example) The suggestion would therefore be that you are more likely to suffer a bird strike below FL100, so you need to stay below the certified speed unless you fancy wearing a seagull as a necklace...



Having said that, the mil are exempt from the speed restriction. What is the certified strength of the average canopy?

[411A]

Personaaly noticed at Khartoum, some years ago, parked on the ramp.
An Ethiopian B727, that suffered a birdstrike at 4000agl, while doing 340 KIAS.
The bird ( a big buzzard I think) went thru the radome, forward pressure bulkhead, broke the First officers left leg, went thru the FD door, and what was left of the bird was splattered all over the first class lounge, just aft of the forward galley.
Not a pretty sight.
Leave the fast below 10 to the military jet jocks.

[Mad (Flt) Scientist]

the mil are exempt from the speed restriction. What is the certified strength of the average canopy?

Considerably greater than for a civil transport category aircraft.

Take a look at a FJ forward windscreen. The one on Hawk is about 1.5 inches thick IIRC - and in the birdstrike tests it deformed so much that there was a fear it would strike the HUD when fitted. It's not WW2-style armoured glass against enemy bullets any more, it's for birdstrike.

(Hawk was about 600kts, IIRC - 4 times the typical commerical impact energy levels)

[fireflybob]

One thing about "high" speed descents is they are less economical from a fuel point of view! Some pilots are under the misconception that staying high in the cruise for longer and then descending high speed will save fuel - this is not the case! It may reduce tech log time so there is an issue with maintenance costs etc but this is the idea of having a cost index on the fmc which will give you the "ECON" speeds which balance fuel burn against time in the air.

Hope this helps - fly safe!

[AV8R-77]

Thanks for the input all.
Basically my reasons for keeping the speed below 250 below FL100 are all mentioned.

VFR traffic close to airfields, bird strike risk on the window, fuel economy. Like fireflybob mentioned, a common misconception that high speed saves fuel. Not possible.......

I hear often that "you will get there faster" now I believe the difference between standard speed and high speed would be less then a minute (unless atc requires an early descend). Now, just about one minute earlier on the ground, is that worth the risks mentioned?

As well you might have a ROD which could exceed 3000ft/min within 3000ft on MSA.

[ahramin]

A note on windshield bird strikes:

FAR 25 aircraft (transport category) windshields have to be able to withstand impact of one 4 pound bird, without penetration, at design cruise speed.

Eagles, cranes, geese, and loons all average at least double this weight.

[alexban]

and design cruise speed will be? ....IAS around 250 kts?....for sure not Vmo
Do a search with 767 ,CDG ,bird strike and you'll see how a small bird can depressurize a big plane,when doing more than 300 kt..

[Threethirteen]

Straying from the Ornithological message for a second: If you plan for 250 below ten (or less in some places depending on Local standard speeds), you reduce your chances of being left hot and high if ATC cut your track miles to run at the last minute.