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Tambaran
4th Mar 2004, 23:57
Just started with another airline and have a question on their acceleration altitude.

Normally company single engine acceleration altitude at 1000'agl unless

1. TOW > 138 tonnes. I guess this is for the 5 minute limit. OK so far.

2. If the T/O performace page says the minimum acceleration altitude is 800' (obstacles) then that is what WILL be used.

It's my understanding that if it isn't mentioned then the minimum accelleration altitude is 400'agl where the 3rd segment starts. If there are obstacles present why lower the acceleration altitude from 1000'. 800 is a minimum but not gospel surely.

One argument given to me is that the obstacle may be further on down at (say) 1200'. This doesn't sound right to me.

It's been a long time since I've done Perf A. So if someone can suggest some good arguments I'd appreciate it.

cheers n beers
:D

swish266
5th Mar 2004, 01:01
Hi.
My Comp S/E accel alt is normally 400 AGL. But at cat C apts like GVA and ZRH we have special proc. GVA is 1500 AGL, ZRH is 800 AGL. Guess at places like this obstacle clr is the main thing...
Hope this helps.

4dogs
6th Mar 2004, 21:23
Folks,

I always get a bit warmed up by these sorts of questions - particularly after a red wine or two. Not because you did ask the question - that is quite proper - but because you felt the need to ask! That means to me that your flight operations management is failing in its duty to you to fully inform you of how they meet their obligations as an AOC holder and as your employer.

Acceleration altitude is something of a tribal secret but should never be so.

Certification requires that the aircraft can complete a flat earth acceleration 400' after take-off at MTOM within the certified engine limits and meet all net flight path requirements. Sometimes AOC holders decide that a second segment climb to the bare minimum 400' does not provide sufficient time for crews to fully consider all of the relevant issues - that usually gives rise to a minimum company acceleration (typically 600/800/1000' dependent on aircraft type) that applies where there are no obstacle considerations. That policy may result in a commercial cost of a reduction in payload.

Where there are obstacles, the acceleration altitude is determined by the highest obstacle underlying the relevant segment, ie the 3rd or 4th or sometimes a 5th if applicable.

The actual payload that can be carried is determined by two things that are a consequence of the acceleration altitude: the engine limits for take-off power/thrust and the gradient required to get to the acceleration altitude.

You should never have to question the required acceleration altitude at any airport from which you may be required to depart - you should always know what that altitude is and you should know whether it is the minimum permitted (company or certification) or if it is an obstacle determined requirement.

If you don't know, then the person to ask is your Director Flight Operations. The answer will be one of life's lessons....

Stay Alive

Tambaran
7th Mar 2004, 03:12
4Dogs, I know all that.

Regarding the asking of questions to the company, I agree. In my previous company that would be fine but this one is lacking. It is a training captain that is feeding me what I percieve to be bull****.
I was just after opinions before I open my big mouth without being fully informed. I don't have access to my books in the near future.

big bus driver
10th Mar 2004, 02:47
I think I remember reading in the WinPEP manual that the accel height can be below the height of the tallest obstacle, providing that obs is sufficiently far away to allow the aircraft to be cleaned up and the climb to be continued at the improved gradient compared to the unclean condition.

WinPEP output shows a min and max accel altitude, which is always printed on my airlines performance page.

BPS for our Boeings just specifies an accel height, which for my company is usually 800' agl but of course dependent on a/d obs, and again is printed on the page.

despegue
16th Mar 2004, 09:47
One advice:

NEVER play "monkey" by blindly follow the procedure.
First perform your memory items, and THEN ask for alt. hold.
Your given Acc. alt. is a MINIMUM for that airport, you will always be safe when going above this altitude. If your aircraft can't climb to 1000'AGL in 5 minutes, then you do have a major problem,e.g. Overloading...

mutt
16th Mar 2004, 19:59
We dont operate the B767-200, but we do operate ALL other Boeing aircraft.

Basically speaking we have three items here.

1: All Engine acceleration, apart from noise abatement, we as an airline set a default value in the FMS, in our case 1000 feet.

2: Engine Out default, FAA limits are between 400-1200 feet. We operate our line airline with an 800 feet default and the associated weight decrement. Our VVIP aircraft use 400 feet but are operated with two Captains, no first officers.

3: Engine Out - Obstacle Clearance, depends on the takeoff thrust rating, 5 or 10 minutes. But it will be a height that will allow the aircraft to level off either above the limiting obstacle, or level-off and clean up then clear the limiting obstacle. We have acceleration heights greater than 2500 feet AGL.


4-dogs... are you a reincarinated richard-4dogs????


Mutt.

XTRAHOLD
16th Mar 2004, 20:45
I do not fly the 767, but the question you posted is pretty general and I remeber my performance analysis for the B-737-800 I used to fly and the differences with the B-747-400 I have the privilige of flying now.
Engine out acceleration altitudes are determined by the operator, FAR 25 states that the minimum altitude to end the second segment is 400 feet AGL thus EICAS warnings inhibits (On aircraft that are equipped with it) will stay that way (inhibited) till passing 400 feet or a preset time so you can concentrate on flying the aicraft on proper speed and path. After those 400 regulation feet, it will depend on the time limit on your aircraft engines (5 or 10 minutes at MAX TO Power) and the paricularities of the airport you are departing from. It is a given that by checking your company's runway analysis tables you are assuring that your takeoff weight on that given day will be such, that you will comply with your second segment climb gradient which as you know, varies from twin to three to four engine aircraft by a set regulation percentage. Furthermore, regulatory agencies want to make sure your departure gradient is at least 2.5% standard or 3.3% if obstacles on the departure path are a factor; if the obstacles are too high or closer, the gradient can be modified accordingly to whatever is required, for example 400 feet per nm equals to 6.67% or a minimum ceiling and visibility is required for the departure so you can see and avoid the obstacle. If you operate out of the US, you will find the required climb gradient of feet per nautical mile published on the different SID for the different runways, to translate that into percentage, just divide it by 60. If you are operating out of ICAO airports it will usualy be in percentage. Now, the performance planners in the airline have to consider if the obstacles are such that a special engine out SID is warranted or not. Some companies will provide you with a table that gives you the climb gradient for different weights and takeoff thrust settings (TO; TO-1 or TO-2) under various OAT temperatures (ISA + 10,15,20,25,30,35), so you can decide if you can continue with the published SID or need to follow the EOSID. but I am getting off track here, back to the engine out acceleration height, most of the operators I know about (Including the current company I work for) use 1000 feet AGL under most conditions for the fleets limited to 5 minutes of TO power and 1500 feet AGL to fleets with 10 minutes TO power. However obstacles do afect these
standard altitudes significantly. For example at max TO power out of SFO on runway 28R, we have an engine out acceleration altitude of 2340 feet and in HKG for runway 7R it is 1340 feet if I remember correctly. This value is published on the same page as the runway analysis performance table. I hope this gives you some additional information to answer your question.:ok:

Dehavillanddriver
18th Mar 2004, 11:08
Despegue

What you are advocating is fine in most places, however in places where there are obstacles further down track, the analysis may well have selected an acceleration altitude that is below the height of the obstacle/s.

In some cases the analysis program calculates a weight that is predicated upon accelerating at a set height, cleaning up and climbing clean over the obstacle. Extending the second segment may lead you into the situation where you extend the 2nd segment distance to the point where you don't have the required obstacle clearance because you had to reduce thrust to MCT before getting the flap all the way up.

This problem is exasperated by 5 minute engines vs 10 minute engines, however the principle remains the same.

Obviously where there are no distant obstacles these issues are not so important, but you end up with a set of rules that apply in some cases, with another rule for other situations - to my way of thinking you would be better having one set of procedures (ie relating to acc alts) so that you didn't have the potential for confusion at a critical moment.

despegue
18th Mar 2004, 16:41
As we fly during the second segment around V2 to V2+15kts., thus very close to Vx and Vy,combined with T/O thrust, we have our biggest rate of climb during that period.
My understanding of performance ClassA is that as you increase your second segment time, you will also increase your altitude over any obstacle further down-route, and thus always be safe.
That is where the second segment is for actually, to get you OVER the obstacle. Third segment is to increase your speed, fourth is to relieve the engines.
So we have 3 priorities here, in the following order:
1) climb to a safe altitude
2) increase speed to be more stable
3) Safe operation of the engines/ E.O. stability

After 400', the main thing to is PF. fly the plane, PNF. Memory items as quickly and accurately as possible.
After this come the secondary priorities.
A request by PF for an action for on the MCP during "memory-item time" will cause much more confusion than levelling off 200' above your acceleration altitude, which I remain is a minimum for that field.

I will gladly correct my views on this if it does appear to be a dangerous thing to do, but then we must also urgently warn the people of DBA, GMI, AB who trained me to do so.

Dehavillanddriver
19th Mar 2004, 01:25
not necessarily.

if you extend the second segment, you are also using up track miles. track miles that the performance engineer may have used to ensure clearance with a distant obstacle.

as you use the track miles you obviously get closer to that distant obstacle. if the analysis has used a level off height lower than that distant obstacle - which does happen for legitimate payload reasons - you start chewing into your obstacle clearance.

if you extend the 2nd segment enough you will run out of the engine thrust limit before you get the flaps all the way up, which means that with the lower thrust setting the 3rd segment will use up more track miles....putting you closer (and lower) to that distant obstacle.

The big issue is that it isn't easy to identify when these distant obstacles are in play....

it would be a real bummer to miss all the close in stuff only to clean up a hill a bit further down track....

4dogs
20th Mar 2004, 08:41
Mutt,

One and the same - the loss of signatures means no email address as per days of old (and 500 or so lost posts!)

despegue,

It appears that "the people of DBA, GMI, AB who trained me to do so" may not have the required knowledge to cater for all circumstances.

V2 is established as the minimum speed that will produce the certification gradients and meet the minimum safety margins over Vs, Vmcg etc. It most certainly is not the best rate of climb or best gradient at that point for most aeroplanes - your flight manual should show you that climbing clean at your enroute climb speed with MCT will give better performance than in the second segment, depending on the take-off flap setting.

The key issue was the acceleration altitude.

If the acceleration altitude clears all obstacles for 30-40 km on the departure track, then thrust settings and flap retraction are not much of an issue - they just will not be in accordance with the procedures envisaged by the certification authorities and they will not be particularly efficient. The vast majority of your operations may well be conducted in such benign geography.

However, some airports have significant terrain issues. If there are obstacles down track, then dehavillanddriver is correct in that maximum take-off weight may be achieved by planning an acceleration altitude below the highest obstacle (with appropriate factors added to the third segment length) with obstacle clearance being achieved in the fourth segment. If that is the case, then extending the second segment and consequently the third segment may result in a very noisy reward for remaining ignorant of the whole story!

I think you need to rethink your approach to the issue.

Tambaran,

I reread your initial question and your response. Since it appears that you already knew the answers, I am confused about what question you really wanted to ask.

Stay Alive,

XTRAHOLD
20th Mar 2004, 12:03
Regarding DESPEGUE's recommendation for ALT HLD when reaching accelerating altitude, I know UAL had that procedure for their B-737's but Boeing's procedural recommendation of opening the MCP window with LVL CHG and setting the clean up A/S will provide you with a slightly positive climb which will enable you to retract your flaps while also conservatively gaining altitude, I have always believed that to be better than to level off.