"Expedite"

[area08]

I have read in MATS part 1 that in reply to an instruction by ATC to "expedite climb" a pilot may reduce the IAS in order to increase the climb rate. What other options are available to the pilot?

Also, how would a pilot "expedite descent"? MATS part 1 states that an aircraft cannot be expected to "slow down and go down". Anyone explain?

Cheers.

[Over+Out]

Expedite climb, equals pull steering wheel back and push power levers forward, use speed for climb.
Expedite descent, equals use the brakes, push the steering wheel forward !!!!!
Steering wheel might be a little thing in your left or right hand !!

[NZScion]

To expedite descent, pilots can also reduce power back to idle (if required), and deploy flap, lower gear, and do all sorts of things to help control speed. The main danger in a descent is not slowing down, but exceeding the max speed for the a/c configuration (be that gear speed, flap speed or Vno.

[Pilot Pete]

A bit of pilot input if I may?

We tend to fly jet aeroplanes at FMC generated "ECON" speeds which take into consideration many factors to produce the most economical profile for a given flight.

In the climb we have limited options for increasing our rate of climb if we are already flying at the ECON climb speed (say about 290kts above FL100). The only real way to significantly increase the rate is to trade airspeed for altitude gain, i.e. we "speed intervene" (over-ride the ECON generated speed) and spin our speed bug back to command a slower speed. In the climb (in the usual climb modes of VNAV or LVL CHG, NOT Vertical Speed, which is different) the aircraft will respond be raising the nose to reduce speed (i.e. give us a steeper climb). It will leave the power set previously (which is pretty close to maximum power) and you will get your expedited rate of climb. In effect we are trading speed for rate of climb. We can reduce the speed gradually and get a moderate increase in rate of climb over a longer period, or we can bring the speed right back very quickly and get a huge rate increase initially followed by a reduced rate as we get close to the target speed.

Some aircraft are better at this than others. I currently fly the 737 Classic and NG and they are particularly bad at smooth transitions in the circumstances described above and can pull more than 1G, which makes it uncomfortable for the passengers. They also pitch quite roughly when you get back to the target speed and 'chase' the required figure in a not very elegant way, again more discomfort for passengers.

The other mode available is Vertical Speed, where we can over-ride the ECON profile and command a particular rate of climb (or descent) in hundreds or thousands of feet per minute. However, if I dial in 3000fpm climb and the aircraft pitches to achieve this, we might not have enough thrust available to keep the speed AND the rate of climb. Speed will decay as the aircraft attempts to follow my commanded vertical speed. On the 737 we have a protection which will prevent speed washing back to dangerously low levels and the aircraft stalling. On the 757/767 that I previously flew, there was no such protection and thus the use of Vert Spd for this sort of climb was not used (in my company).

So, what you have to understand is there is a limit to what we can achieve with the thrust/ speed available. What we find useful when being asked to expedite is the level to which you require us to expedite; say we were climbing through FL200 and we were cleared to FL280 and you wanted us to expedite through FL230, that would be very useful as we could trade the speed for a high rate until FL230 and then trade the rate to regain our ideal speed for ECON and then continue the climb at the best ECON rate.


In the descent we usually use the best ECON descent profile, which is an IDLE descent started as late as possible in the prevailing conditions. This obviously won't always fit in with the ATC environment. If we are are above FL100 our speed can be quite close to maximum (at least it is much higher up) and therefore to increase our rate of descent our options are limited.

If our ECON descent speed allows us a 'margin' to max speed (which is does, the lower you get the bigger the margin), then the ideal way to increase the rate of descent is to 'dive' the aircraft down using a greater speed. In this case the aircraft pitches down to accelerate to the increased speed (with the thrust at idle throughout), so initially you will get a much increased rate of descent as it accelerates, until it reaches the new commanded speed and then the aircraft pitches up a bit to maintain this speed and hence the rate will fall away somewhat.

To increase descent when you can't speed up any more, you can deploy speedbrakes (panels on the top of the wing which reduce lift), which on many types can induce a bit of buffetting and thus slight discomfort for passengers, so we prefer not to use them if we can avoid to.

Another point worth noting is that speedbrakes are more effective at higher speed and much less effective at lower speed. For instance, on the 737 they do little for the rate of descent below 250kts and virtually nothing back at 210kts.....other than buffet!

Other options are of course increasing drag by using landing gear, but there are limit speeds on all types and unless we are on final approach (or close to) it is pretty undesirable to use the gear for such purposes. What we really don't want to do is drop the gear to increase rate and then later on have to fly level! Obviously fuel burn would go through the roof and it creates lots of noise for the residents beneath us too, so really landing gear for increased rate is not an option IMHO.

As for using flap to increase rate of descent, well, again not really an option. Flaps are for increasing LIFT at reduced speeds. Our airline does not permit the use of flaps as speedbrakes as it puts such a strain on the flap tracks and leads to increased maintenance costs and undue wear.

In modern jet transport aircraft we have wings which are designed to be most efficient in the cruise (where we spend the majority of our time), thus they are not at maximal efficiency when close to the ground at typical landing speeds. That is why we have such big flaps to increase the surface area (and thus lift) at slow speeds and allow us a pitch that will let us see where we are going near the ground. The wings really are VERY efficient at producing lift, so when we are descending we are in effect gliding (at idle power). In order to reduce speed we need distance (think of an oil tanker with so much inertia to overcome). We have a similar problem. Say I am in my 737 at FL100 at 300kts. If I want to reduce speed to 250kts, in level flight, I need approximately 5nm to achieve this (1nm per 10kts of airspeed). To reduce further to 210kts, in level flight, I require another 4nm. Remember, this is IN LEVEL FLIGHT with IDLE THRUST. If you also want me to descend, then Houston, we have a problem!

We work on a rule of thumb for an idle descent of 3nm for every thousand feet of altitude to lose. This is at a CONSTANT AIRSPEED. So, to descend from FL200 to FL100 we will require 10 x 3 = 30nm. If you want us to reduce speed from 300kts to 210kts as well, then it will take another 9nm to achieve that. So in effect we need 30 + 9 = 39nm (call it 40nm for simplicity). Various factors will affect what we actually require, a headwind will reduce it, a tailwind increase it and so on.

The best way to do it is to descend first and then to reduce speed, but if you want both at the same time you will get a very small rate of descent and a very slow reduction in speed. Remember, these things are real slippery beasts, so trying to slow down whilst descending is particularly difficult. Speedbrakes can help, but remember they are most effective at higher speeds and much less effective at lower speeds. It is all a case of a trade off, one or t'other, both is hard!

Anyhow, hope that helps.

PP

[eyeinthesky]

PP: What an excellent and clear reply: thanks. I hope as many ATCOs as possible read this as some of them seemd to have no understanding of Econ speeds and the rest of it. :D

[area08]

Fantastic reply Pilot Pete. Thank you very much.

[the Shue]

Pilot Pete, very interesting and informative. Thanks for the time taken to reply.

[VoxPopuli]

I think in a case were expedite climb or descent is used, the speed becomes immaterial. The emphasis is on up or down, not forward. That being said, I also think the whole expedite thing is vague as their is no restriction coupled to it. One pilot's expedite is another one's cruise climb.

[fireflybob]

Pilot Pete, as usual very erudite!

Couple of points I would add:-

Angle of climb (height gained for horizontal distance travelled) and Rate of Climb (height gained versus time) are not the same thing. If ATC want us to cross a geographical point in the climb above a certain level then the best ANGLE of climb speed is what is required rather than best rate of climb speed (obviously zoom is a factor as Pete has already mentioned).

I see some pilots who are confused about the difference. For example if the MSA on departure is high (for example departing some Italian airports and then turning northbound across the Alps) then, all things being equal, the speed in the climb should be best angle (the FMC will give you this - around 240 kt ish on the B737-800 at average weights) until the enroute MSA is achieved.

Regarding regaining the profile when held high on descent, I believe that when in the medium to high levels (above about 15,000 - 20,000 ft) increasing the speed is effective at bringing the a/c back on profile since the drag is a function of the TAS squared and since you are high the TAS is high so this works. However when you get down lower this doesn't work so well so if I am high on profile below circa 15,000 ft I will nearly always go for the speedbrake. In the lower levels if you are high and increase speed you don't do much to catch the profile and you are still going fast at the bottom and then you need more miles to slow up so nothing is achieved. Also most companies like 250 kts max below FL100. If you are close in then you need to slow up and get some flap down because what you want then is ANGLE of descent although as Pete says Boeing don't recommend use of flap as a "speedbrake" due flap wear etc.

Hope this makes sense - its been another long day!

[Tail-take-off]

Slightly off thread, but when ATC ask for a "good rate" what sort of minimum rate do they mean? Of course bearing in mind that it is often requested immediately on departure when speed is low so trading speed for height is not an option.

[The Many Tentacles]

A "good rate" isn't anything I'll request as it's too ambiguous. "Expedite" means the same thing to both pilots and ATC, increase or decrease the rate of climb or make the turn tighter depending on what I've just told you.

I always remember being clipped around the head by my instructor the first time I used "good rate" because the good rate for the pilot might be an extra couple of hundred feet a minute or they're already using what they consider to be a good rate, which in the circumstances is not a good rate for me.

I know the term is used and I know that when people are saying it, they want you basically to expedite your climb or descent through the specified level. It's an example of non-standard phraseology that has crept in.

I don't know if that all makes sense, but in my head it does.:)

[BOAC]

A 'good rate' after departure is best achieved by keeping the speed back after flap retraction at (about) min clean speed rather than accelerating to 250kts or whatever. Deletion of any 'climb reduction' in the system also helps. This of course only helps with the first few 1000' of the 'expedite' but often helps to clear i/bound traffic at LGW when you are looking for an 'early turn' towards Jockistan and gets you up above 8/90 in good shape. It works well.

[Quokka]

Love the work of the A310 yesterday, who, at around F200 on climb, when given "expedite through F310" proceeded to reduce his Rate-of-Climb from 1800FPM to 1000FPM in less than a minute... :ugh:

After changing the plan and cutting off the climb of the A310 and instructing the B767, which was on a converging track a few thousand feet beneath the A310, to "expedite climb through F280" the B767 managed to ramp up his Rate-of-Climb from 2000FPM to over 3000FPM and rocketed up past the A310... :ok:

[eyeinthesky]

QUOKKA:
If you think asking someone to 'expedite' for 11,000ft is reasonable, then you deserve everything you get! := I hope you're not basing your separation on this?!

Read the posts earlier about how expedite is achieved and then see why what you asked was daft.

[BOAC]

As fireflybob has explained, there is a difference between 'best angle' and 'best rate' and I suspect both some pilots and a lot of controllers are a bit vague about the difference. It is a great help if we know the level through which or the point by which you want the 'expedite'. Be aware that asking for an 'expedite' over a large altitude band COULD result in a pilot accelerating the a/c to best rate of climb speed which might cause a moment or two of heart-stopping on the screen as the rate of climb initially falls during the acceleration, so be careful to know what you want and how you ask for it!

[Airbus_a321]

In the sophisticated AIRBUS we use the EXPEDITE button on the FCU e.g. to comply with ATC request to expedite. We use the expedite button both for CLIMB and for DESCEND. Just push EXPEDITE - that's it - and the controller is happy :cool:
Nice and safe feature. Really excellent this aircraft. I love it:ok:

But not to forget: := it's just an "energy" button NOT an "extra power" button. If you Expedite in CLIMB and the speed comes to Green Dot Speed the climb-"game" is over and out.

[LapSap]

What ever it means, some ATCs use it way too much to make up for sloppy control technique.

[1985]

What ever it means, some ATCs use it way too much to make up for sloppy control technique

I agree but also at times its a very useful tool. If a couple of aircraft have to "expedite" to stop them from getting the dreaded stepped climb and at the same time the conflicting traffic can be descended to make their levels or to allow other traffic to make their levels whilst streaming then its a good technique.

If someone is telling every aircraft to expedite then thats poor knowledge and technique, but a few every now and then is using the tools at their disposal to achieve their aim.

[Tail-take-off]

Airbus_a321

Ifly the A320 series too & I agree with what you say. Unfortunately we have some pilots who fly the 330 as well & that has a "level off" button where the EXPED button is on the 320. The Fleet management has therefore banned the use of the EXPED button in case one of the sky gods who is deemed capable of flying both types gets confused in an emergency descent & presses level off instead.

I appreciate the all suggestions above as to how to acheive a good rate (I've used them all in the last decade or so including the EXPED button) but my point was actually what rate of climb will ATC expect when the ask if you have a good rate available or ask you to expedite. You can do what you like in a 321 at max take off weight to give the best rate available but it is certainly not what I would call a good rate.

[Knackers]

I don't allow my trainees to use "expedite". It's a useless phrase which achieves....what? You never know what's going to happen. I agree it's sloppy controlling.

[Quokka]

It's a phrase I'm never comfortable using... but in this particular situation, both crews, English-as-a-second-language pilots flying for airlines that are banned from flying in Europe... for a very good reason.

You can attempt to issue a requirement but often the reply is... "confirm you wish us to track direct to.....?", or worse still a readback of direct to a waypoint that you never mentioned in the requirement (and this occurs often). The sort of crews who when asked for a spot wind, will give you their RADAR heading...:ugh:

You find that after several attempts to issue requirements, you have to resort to Keep-it-Simple principle. The alternative is a Step Climb (which no-one likes) or a 90 degree turn (simple and effective...when you have the room).

Workload becomes a factor when you have multiple Step Climbs in progress, aircraft being vectored and inadequate receivers.

Unfortunately, we don't have the "luxury" of the Air Traffic Control environment in the First World...