Thank you for the replies. That's the beauty of PPRUNE, we are globally connecting as operators in our magnificent industry.

I am sure the founder, Danny Fyne will be proud of this and create discussion of items that are not really mentioned in official documents and non official ones.

From Europe, I personally know and witnessed that our founder would have conducted many high speed descents. Yes agree that workload can rise if not properly briefed, managed and flown but at the end of the day we have to be efficient in what we do behind safe and secure.

I question why they are not deemed efficient even though the thrust levers close at ToD and as part of a CDA possibly spool up at 1400ft all to become stable. Lowering the EGTs and saving fuel make them all worth doing and also makes us fly the a/c, which truthfully is becoming a lost skill.

In Europe many a charter outfit have save thousands of pounds in the process and have at times saved airlines from bankruptcy by being a sound effecient pilot.

So back to the original question, assuming no ATC speed restriction and deletion of 250 below 10000 there is no restriction on the NG?

Thank you

Vmo is 340. fini.

Simmer? Lordy.

Actually I'm a 767F captain.

But I was an MD-11F captain when I hit a bird outside Quito at 330 kts. Terrain was around 10k msl so we were definitely in birdstrike territory above ten. Cost the company a radome and a bunch of other damage.

I've also hit a bird at 250 kts in a King Air, hit another at ~170 knots in a DC-10, and at 130 knots in a 767, last month, in the flare at Changi.

With a wide spectrum of data on this, I do 250 or less below ten. Always. Maybe above ten if the terrain is super high.

I don't buy the 'cost saving' line, lest we ignore Boeing's cost index. Whenever I've seen it done on the line, the driver was a pilot who thought flying faster was a sign of skill. The same people always find themselves hot and high.

I prefer to 'see and avoid' at <250 kts under 10,000 feet. I'm obviously uncool.

I don't buy the 'cost saving' line,

Years ago it was shown to me, via paper calculations, that descending at hi-Speed below FL100 does not save fuel or time; therefore is not more efficient. Hi-speed from TOD does save time, if you get it correct and ATC does not intervene. It can be very embarrassing if you 'plan/brief' a hi-speed descent from TOD with no buffer an ATC turn you in shorter. Up creek with no paddle and sweaty palms come to mind. Speed brake the whole way, gear out early, flaps out on limits and a dive in landing config. Do it once and never do it again. Was it really worth it? You could ask ATC for more distance; so they put you in sequence behind a heavy, instead of in front, and your 'more efficient descent' just went to the opposite.
Easiest way to save time & fuel is a shorter turn in with a CDA to 1000'. More relaxing for those down the back, and certainly for those up front.

Underfire, the FMC speed coding to 240 its below FL 100 is nothing to do with ATC, its a VNAV coding to allow deceleration. :

Normally, the target speed is economy speed above the airspeed restriction altitude and 240 knots below that altitude, until deceleration for approach. VNAV will not permit descent below the airspeed restriction altitude until the airspeed is at or below the restricted value plus ten knots. The start and end of the airport speed restriction deceleration segment is shown on the map as a green open circles with no labels.

12-11.31.24 B-737NG Operations Manual Part B 38/26 SEP 13 Volume 5

Sorry Huck, I read something into your post that wasn't there.

Rat 5

I bow to your greater knowledge. I was merely going on my understanding of the basic Boeing CI, which will give climb, cruise and descent speeds to prioritise money over time, or vice-a-versa.

With CI 30 giving a 270 kts idle descent and CI 6 giving 245 kts, one presumes that the earlier TOD and slower idle descent is more efficient in terms of cost. Naturally, without ATC interference and with wholly correct FMC inputs, both would theoretically give an idle descent to the final approach.

Ergo, maintaining high speed below FL100, unless the restriction were removed before TOD, would burn extra fuel.

Absolutely no prob.

High speed saves time but will increase cost. In descend. Climb at eco speed below 10000 ft saves fuel.
I've been flying long enough to remember when there was no speed limit below 10000 ft. High speed was pretty much SOP, and it was not a big deal.
250/10000 ft was introduced by ATC.
So now high speed below 10000 ft is a near death experience?
I have an image in my head of white knuckled pilots with sweat running down their faces while they blast through the air at 280 kts. Are we going to make it?

Apparently, I'm lucky to be alive.

Here, the main use of "above ECON" speed is at ATC request to make the inbound flow work better. It might cost a bit of fuel but will mean that I will not mess around possibly 5 aircraft behind me. Optimally, you'd clear the 250/10k before Top of Descent. If you can't, there are still benefits for all involved.

Only if fuel is expensive... Extra flight time costs money as well.

You guys using different physics than the rest of the world??

Of course high speed below 10,000 saves time. Using 310 kts instead of 250 kts from 40 nm to 20 nm saves you .9 of minute.

Speed vs altitude is the name of the game. 250 kts at 10,000 at 40 miles to go, is a great efficient and quick energy fix. Crossing it at 310 kts means you'll have to use drag to get rid of the excess energy. Here's the solution - for every 30 additional knots be approx 1000' lower. IE - 280/9000/40 and 310/8000/40 are about the same total energy.

You can double check this by removing the FMC's 250/10000 restriction and inserting a fix at 40 miles to go. Then put the different descent speeds on the FMC's descent page and see how much lower you'll be for every additional 30 KIAS. It's about 1000'.

There are places and seasons where I don't do 'high speed' below 10,000. The majority of the time it's John Daly time - "grip it and rip it." (Don't overthink it, just do it)

250/100 is a speed restriction due to airspace. It also helps prevent High energy approaches.

Putting 250/100 in the FMC does not make it increase speed from CI6 245 to 250. It merely allows for the airspace speed limit/company limit to be adhered to if we are asked to fly faster than 245 above 100.

If you ignore the distance to the runway 250/10,000 does not reduce high energy approaches. 250 kts below 10,000, at 5 nm to go, is too much energy. 250 kts below 10,000 at 50 nm to go, is an easily managed amount of energy.

It's a three headed monster - speed, distance to go, and altitude. The various combinations provide a low, good, or high energy state.

Easily managed can go to 'ah, bugger' quite quickly in busy airspace!

Yep, the appropriate cost index should vary between airlines, aircraft types and even routes. Here in Europe, fuel is a high cost, so the CI is often low. In my airline, salary and maintenance costs are tightly controlled, hence they're less important than fuel. Moreover, there's little emphasis on scheduled arrival times in my company, so they'd rather we stuck to the most fuel efficient flight profile.

and then connecting passengers issue joins in the party of the CI..

framer, sorry, but the system defaults to 240kts below 10K in VNAV. If you bust 250kts below 10K, it will go to LVL CHG. I do get to do quite a bit of sim work, first desktop, then the full motion to test RNP procedures.

737 FCOM: 11.31.34
http://i.imgur.com/bparzaR.jpg
http://i.imgur.com/u4V5zH5.jpg
http://i.imgur.com/O8FLYYd.jpg

Somehow I'd guess 3/4 of this lot could not manage an idle descent from altitude to save their lives without furiously typing requests to the VNAV gods.


As for the high speed at lower altitudes, it depends. My need-for-speed is tempered by the pics of one of our 767-300's that took multiple bird strikes >10K out of CDG. I believe the speed was north of 340KTS. The jet looked like it took more than a few rounds of 20MM cannon hits along with a bloody carcass that punched through the left forward cockpit pressure bulkhead and ending up splattering over the Captain's flight bag.


4-5 lbs birds, but my memory is a little weak on actual size. Choose wisely, Tweety doesn't have TCAS. :E

I can see three different possibilities Underfire;
1/ you were in a rush and what you wrote above was in error.
2/ you operate FMC updates that are fundamentally different to any I have seen since 10.4
3/ You really shouldn't be validating RNP procedures for any passenger carrying airline until you understand the basics.
Which one do you reckon?

While the programmer boffins surely appreciate the promotion, am I not alone in nearly always having a rough idea in mind for cross check, just in case 'ye gods' have gone mad? And for those times when it's not perfectly clear, a visit to the altars of Father Time and Maths should help the lost find their way.