Fast And Low In Jets?

[-1000AGL]

Some countries (and controllers) allow jets to fly fast at lower altitudes. (Above 250 KTS below FL 100)
Some pilots claim that this have many disadvantages and risks. Can you share some thoughts of the risks for passenger jets? I am thinking of speeds above 250 kts below FL100 and stuff like bird strikes, CFIT, VFR traffic separation, GPWS/TCAS warnings, fuel consumption and so on…
(I was trying to find information or recommendation from Flight Safety Foundation about high speed at low altitudes but could not find anything.)

[411A]

Advantages.

For aircraft at heavy weights, the higher speed is more efficient.

Dis-advantages.

Potential bird strikes.
Recall some years ago noticing an Ethiopian 727 at Khartoum, parked on the ramp.
The large bird had penetrated the radome, forward pressure bulkhead, FD entry door, and the remains of said bird were in the FC lounge.
Not a pretty sight, for sure.
The idea of 340KIAS at 4000agl may not be all that good for ones health, with big birds (feathered variety) in the vicinity.:}:uhoh:

[guclu]

You are correct about your ideas.

Considering bird strike the force applied to the a/c is

F (force) = k (constant) x m (mass of bird) x V x V (speed of bird plus the a/c; hence neglect the speed of bird)

So speed has a squared effect on the impact. And if we calculate :

250 kts = 128 meters/second
300 kts = 154 meters/second

So for k = 1 and mass of bird = 1 kg the forces are (just to see):

F(250 knots) = 1 x 1 x 128 x 128 = 16384
F(300 knots) = 1 x 1 x 154 x 154 = 23716

One more disadvantage is the a/c becomes to act like in turbelence if you increase your speed at low altitudes near Vmo. So that is also not good for passenger comfort and also the a/c.

But on the other way, most of the birds live below 6000feet., and some very busy areas (London, Paris, Schipol, ...) can not let you climb above 10000 but they want you to deliver to the next sector as soon as possible so they let you fly at speeds above 250Kts. Also during your approach for sequencing they might require you to fly greater than 250.

Hope it helped.

Guclu Ulgenalp

[BOAC]

Indeed! So much so that a large bird hitting a 550kt Harrier (or was it the other way round....) a while back off Belize moved the Pegasus engine rearwards in the frame shortly before the pilot went swimming.

[LGB]

You don't want to fly too slow either. Some jets are so sluggish they risk getting bird strikes on the trailing surfaces :eek:

[click]

Vibro-acoustic Disease. Turns yer soft tissue to cartilage and makes you permanently grumpy. Shortens the life span and accelerates the arthosclerosis, permanent mood swings, mostly to the nasty side.

We are just starting to fund a project with one of our 'flying Doctors' on this subject. Seems the worst offenders (for our fleet) are the A310's at low altitudes and high speed. Slowing down diminishes the effect on the human body. Our doc mentioned that's the reason why one feels like a spent cartridge coming off a day's work whereas spending the same amount of time as an earthbound working stiff leaves one somewhat useful for other carnal pursuits.:E
With that, I am off to enjoy my day of rest:}

[westhawk]

I have read NASA and FAA reports citing the benefits that greater speed flexibility below 10,000' has on traffic flow management and airport capacity. The FAA's much talked about "Freeflight" concept also makes reference to this practice possibly being expanded in the US to include many more terminal areas in addition to KIAH. I also read ALPA's birdstrike/wildlife hazard commitee reccomendations. They take the position that speed should remain limited to 250 KIAS below 10,000 in view of the birdstrike hazard and make several reccomendations to mitigate the hazards. With flight safety and economic interests in apparent conflict, I expect debate on this issue to continue far into the future. I tend to believe that more accurate real-time bird tracking would be useful in making a proper threat assessment. I have been lucky in that my three birdstrikes were small birds hit at low airspeed and did no damage to airframe of engines. In consideration of some past accident reports, I realize it could easily have been otherwise. Earlier posts have cited the kinetic energy involved. One more thing to consider!

Best regards,

Westhawk

[PPRuNe Radar]

Where we, as ATC, allow faster speed than 250Kts in the UK then it is only a relaxation of the regulatory speed restriction for that airspace. If the pilot has an airframe or company limit, then our lifting of the restriction does not mean they have to go faster than they want to.

[EI-MICK]

I always hear various pilots asking for "free speed" on a climb or descend,i presume this is the acceleration of the aircraft to climb speed below FL100??? ATC never seem to have a problem with it at my local airport

[LGB]

Discussed many times before, see for instance these threads:

http://www.pprune.org/forums/showthread.php?s=&threadid=134138

http://www.pprune.org/forums/showthread.php?s=&threadid=145831

http://www.pprune.org/forums/showthread.php?s=&threadid=180549