Mr Spaceman
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What's This Airline Pilot Going To Do? - Takeoff?

Thu Jun 12, 2003 5:40 am

Hi guys.

Here's a quick little question of curiosity.

In the first photo below, you can see an airliner that appears to be taxiing into position for an intersection takeoff on runway 04R at France's Nice Intl Airport (NCE?LFMN). I don't think it's going to continue taxiing across the runway because there's no hangars located over there. (there's no hangars in the second photo.)

What I'm curious about is whether or not the pilot of this airliner is infact going to leave a few thousand feet of runway behind him and take off, or if he's perhaps just going to do a high speed taxi run after some maintenance ..... for example.

What do you guys think the pilot of this airliner is going to do?

If he is going to take off, why do you think he isn't using the whole runway? It sure doesn't look like a small aircraft to me. I'd guess it's the size of an A310 or 737.


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Photo © Denis Roschlau



In my opinion, here's a view of the correct way to taxi into position for takeoff while driving an airliner ........from the very end of the runway! Big grin


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Chris  Smile
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Leezyjet
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RE: What's This Airline Pilot Going To Do? - Takeoff?

Thu Jun 12, 2003 5:55 am

Yes he is most likely doing an intersection departure.

Most a/c do not require the full length of the runway to take-off anyway. If you spend alot of time at airports you will regularly see a/c doing intersection departures (where it is possible).

Example, if the airport has an 12000ft runway and the a/c can take off in 6000ft, then it could quite safely take off from just under half way down the runway, so if you are running late or have a slot to make, why waste time going all the way to the end when you don't need to ?.

The length of runway required for takeoff varies for every single flight. Things like a/c weight, any defects such as a locked out thrust reverser or brake unit, air temperature, altitude of the airfield itself, wet or contaminated runway can all influence the TOD (Take off Distance Required). Most a/c also do not use full power on take off and the power setting used on take off also determines the required length to get airborne.

 Smile
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aloges
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RE: What's This Airline Pilot Going To Do? - Takeoff?

Thu Jun 12, 2003 5:57 am

Maybe his flight is empty (like off to maintenance) and he wants to save some taxi time.
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aa61hvy
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RE: What's This Airline Pilot Going To Do? - Takeoff?

Thu Jun 12, 2003 6:48 am

Yeah the pilot knows what he is doing, there is no need to taxi all the way up to the start of the runway if he doesn't need to.
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Mr Spaceman
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RE: What's This Airline Pilot Going To Do? - Takeoff?

Thu Jun 12, 2003 7:16 am

Hi guys.

OK, so you think it's very likely that these pilots are about to apply takeoff power and are going for it! Great, I wish I was onboard, although I'd rather him use all the real estate behind him! Big grin

The main reason why this photo caught my eye and made me curious, is because I've only seen smaller, lighter Dash-8's, ATR-72's, bizjets, etc, depart from a taxiway intersection at Toronto's Pearson Intl Airport (YYZ). The larger airliners always use the whole runway.

>Leezyjet, I understand that most aircraft don't require the full length of a runway to be able to safely takeoff. I'm aware that jet aircraft don't need to use full throttle to get airborne (like GA birds do). Instead the pilots punch a whole bunch of variables into their computers and receive the power setting that's nessesary for the conditions at the time. Plus there's the balanced field length numbers to calculate.

I also know that the pilots would be very upset (to say the least) if they suddenly experienced a major malfunction just before reaching V1, had to abort, but couldn't stop on the remaining runway and slid into the drink! The 2000 feet of runway they didn't use would have come in handy then.

Perhaps this airliners is very light or even empty as mentioned by Aloges.

I know, I'm only talking about What If?


Chris  Smile
"Just a minute while I re-invent myself"
 
Leezyjet
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RE: What's This Airline Pilot Going To Do? - Takeoff?

Thu Jun 12, 2003 8:31 am

"if they suddenly experienced a major malfunction just before reaching V1"

V1 is the point where they should still have enough runway left to stop on, so they should still be OK if they have a malfunction before V1.

"Instead the pilots punch a whole bunch of variables into their computers and receive the power setting that's nessesary for the conditions at the time. Plus there's the balanced field length numbers to calculate."

Not quite, they look it up in mauals that detail the power settings/take off speeds based on the variables for that specific flight on that runway at that airport.
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Mr Spaceman
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RE: What's This Airline Pilot Going To Do? - Takeoff?

Thu Jun 12, 2003 9:17 am

Hello Leezyjet.

You are correct, of course, about V1 being the point in speed where the pilot has to either abort the takeoff due to a problem so he can safely stop on the remaining runway, or continue to Vr and be commited to a takeoff where any problems will be handled as an inflight emergency.

If the pilots of this airliner have a problem just before V1, they should be able to stop on the runway IN A PERFECT WORLD! Big grin However, if there's a malfunction that affects the airliner's ability to brake, deploy it's thrust reversers, extend it's ground spoilers, etc, then the flight crew and passengers could be going for an unscheduled swim.

I'm sure these pilots are on their game, and an uncontained catastrophic engine failure is highly unlikely, however, I know that a lot of pilots feel that the best way to start ANY takeoff is with the tail hanging over the grass!

Chris  Smile

"Just a minute while I re-invent myself"
 
UAL747
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RE: What's This Airline Pilot Going To Do? - Takeoff?

Thu Jun 12, 2003 9:27 am

BTW, that's a 737 not an A310.

UAL747
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goboeing
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RE: What's This Airline Pilot Going To Do? - Takeoff?

Thu Jun 12, 2003 12:03 pm

Takeoff technicalities aside, I'd want to have that few thousand feet or so available in case of an aborted takeoff if I were PIC.

I'm only a GA pilot, but it's more comforting to lift off seeing 3000' left than seeing trees approaching. If the engine were to quit at 30' in the second scenario, it would certainly be more challenging.

Nick
 
IMissPiedmont
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RE: What's This Airline Pilot Going To Do? - Takeoff?

Thu Jun 12, 2003 12:47 pm

I have never seen a large tranport do an intersection takpff. Of course I've only been watching aircraft movement for 35 years.

I have, however, seen just such a movement when the active changes. And considering the proximity of the approaching flight, I suspect that is possible.

Speculation only though.
The day you stop learning is the day you should die.
 
FredT
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RE: What's This Airline Pilot Going To Do? - Takeoff?

Thu Jun 12, 2003 4:01 pm

You can't count in reversers for a RTO/when calculating V1. I'd assume the same holds for spoilers.

With the current job climate I think a lot of pilots feel that taking off right away from an intersection, if able to do so safely, is better than explaining an extensive delay to beancounters and management later.

Airliners are intended to make money, and the money is not made sitting as number ten for takeoff on a taxiway. Yes, the end of the runway would add margin but also cost money. Extending the runway to twice the current length would also add margin...

As much as the air transport industry denies it, within reasonable limits safety measures do have to be economical. Everything can be made safer - but the cost increases exponentially.

Cheers,
Fred
I thought I was doing good trying to avoid those airport hotels... and look at me now.
 
modesto2
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RE: What's This Airline Pilot Going To Do? - Takeoff?

Thu Jun 12, 2003 11:32 pm

Intersection departures are fairly common. While aboard a WN 737, we performed an intersection departure at OAK. However, I think this decision was also motivated by the delayed flight!
 
Rick767
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RE: What's This Airline Pilot Going To Do? - Takeoff?

Fri Jun 13, 2003 2:17 am

Fred T makes an excellent point. There is a distinct difference between less safe and unsafe in this case. The line between the two is usually drawn by what we refer to as "Aircraft Limitations", in this case "Performance Limitations".

There was a similar discussion last month on the pros and cons of intersection departures:

http://www.airliners.net/discussions/tech_ops/read.main/60652

In one of the longer posts towards the bottom I described a situation where I have done an intersection departure which was actually more safe in performance terms than a (derated thrust) full-length departure (reaching V1 less far down the runway than doing a full-length takeoff).

In all cases the calculations are done in advance and performance data is checked to ensure that thrust setting, flap setting and V speeds are used which provide a safe margin in the event of a high speed abort, or high speed single engine continue.

The calculations for RTO do not take account of reverse thrust (which we would most certainly use) but do assume maximum braking and full speedbrake deployed.

Like FredT put it, "everything can be made safer – but the cost increases…". An absolutely true statement. We could double the size of every runway in the world… and takeoffs would be safer, we could fit EGPWS to every airliner in the world and flying would be safer, we could install an ILS at every airport in the world and flying would be safer. But a line has to be drawn (that line I was talking about before). It is based on a balance between economy and safety, and provided you stay on the right side of that line, all will be well.

The first line of our company standard operating procedures sums it up nicely:

"The crew members should co-ordinate their actions to ensure that the aircraft is operated safely and efficiently at all times."

Safely, and efficiently. In that order. In other words, provided we don’t risk the first, we must strive to achieve the second, at all times.

The thinking these days is very much removed from the pilots duties simply being to get the aircraft from "A to B" safely. Today the crew are expected to take commercial considerations into account at every opportunity to achieve the most efficient trip between A and B. That involves derating takeoff thrust, tankering fuel in some cases, selecting and negotiating more optimum speeds, altitudes and routings wherever possible, etc, etc…

All the while, safety is never compromised, but efficiency is enhanced. Have no doubt that in the future, this will become the role of the pilots more and more.

Anyway this post became longer than I intended!
I used to love the smell of Jet-A in the morning...
 
Woodreau
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RE: What's This Airline Pilot Going To Do? - Takeoff?

Fri Jun 13, 2003 7:12 am

According to the airport chart there's 8100ft / 2470m of runway available from the A3 taxiway where he's starting his intersection takeoff on 04R.

Just an info tidbit.

Cheers  Smile
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POSITIVE RATE
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RE: What's This Airline Pilot Going To Do? - Takeoff?

Fri Jun 13, 2003 2:12 pm

I didn't think a 737 was capable of an intersection departure until i was onboard one- a 737-700. We took off from the half way point of the runway, and this was in February(summertime) with a nearly full plane. How does that old saying go?- "the 2 most useless things in aviation are 1) the runway behind you and 2)the fuel you didn't bring along.
 
Rick767
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RE: What's This Airline Pilot Going To Do? - Takeoff?

Sat Jun 14, 2003 1:39 am

"the 2 most useless things in aviation are 1) the runway behind you and 2)the fuel you didn't bring along"

That's all very well in General Aviation, with single engine aircraft and light twins, but when you start talking about the commercial world of flying it simply doesn't work.

By that theory we would takeoff with full fuel tanks on every flight and never depart a runway from an intersection even where 9,000ft+ of runway remains available!

Like I said before, commercial considerations dictate these procedures for airlines, and so provided safety is not compromised we will depart with minimum legal fuel for a trip (generously sufficient in most cases anyway) and where appropriate we reduce ground delays by utilising an intersection departure provided the figures work out.
I used to love the smell of Jet-A in the morning...
 
Mr Spaceman
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RE: What's This Airline Pilot Going To Do? - Takeoff?

Thu Jun 19, 2003 4:02 am

Hi guys.

Thanks for your additional thoughts and info about this question of curiosity.

I'm in the same boat of thinking as Goboeing & IMissPiedmont. As a GA PIC, I'd want to use all of the available runway for a takeoff .... just incase, and I've never seen a large airliner depart from an intersection ..... thus the curiosity and the question.

However, the pro's in this forum have cleared many things up with regards to departing from an intersection in a large airliner.

I've learned that intersection departures are fairly common. A lot more than I would have ever thought.

> FredT, Thanks for explaining that thrust reversers (incase of an RTO), are not part of the formula when calculating a V1 speed. This make good sense to me now. The way I see it, what's the sense of including TR's ability to help braking during an RTO when it's very possible that the RTO was cause by an engine failure .... thus no TR thrust is available. (from at least one engine).

Question: If an engine failure is the cause of an RTO (rejected takeoff), will the thrust reverser on the good engine(s) still be used? Or would this cause to much difficulty in directional control while on the runway?

> Rick767, Thanks for your very interesting explaination and your link to the previous thread (I read some of it when it was active).

I think it would be great to watch a 767 perform a full-length departure with the use of derated thrust, and then watch another 767 (of the exact same weight) perform an intersection takeoff with 3,000 less runway .... only to rotate and lift off much earlier down the runway! That would get some people thinking.

> Woodreau, Thanks for the info about how 8100 feet is available from the A3 taxiway that the pilots were using.


Chris  Smile
"Just a minute while I re-invent myself"
 
m717
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RE: What's This Airline Pilot Going To Do? - Takeoff?

Thu Jun 19, 2003 4:16 am

"You can't count in reversers for a RTO/when calculating V1. I'd assume the same holds for spoilers."

Actually the spoilers are counted on when calculating V1. So are the brakes and anti-skid system. If any of these are inop, then there is a takeoff distance penalty. Accelerate-stop distances (part of the overall picture when calculating takeoff performance) are predicated on maximum anti-skid braking and spoiler deployment, but do not consider reverse thrust.
 
Mr Spaceman
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RE: What's This Airline Pilot Going To Do? - Takeoff?

Thu Jun 19, 2003 4:30 am

Hi again

Here's one last thought I forgot to mention.

>> FredT and Rick767. These comments by you guys in response to my original question, really helped to put the answers into perspective for me.  Big thumbs up

>> With the current job climate I think a lot of pilots feel that taking off right away from an intersection, if able to do so safely, is better than explaining an extensive delay to beancounters and management later.

Airliners are intended to make money, and the money is not made sitting as number ten for takeoff on a taxiway.

As much as the air transport industry denies it, within reasonable limits safety measures do have to be economical. Everything can be made safer - but the cost increases exponentially.


>> The first line of our company standard operating procedures sums it up nicely:

"The crew members should co-ordinate their actions to ensure that the aircraft is operated safely and efficiently at all times."

Safely, and efficiently. In that order.

Commercial considerations dictate these procedures for airlines, and so provided safety is not compromised we will depart with minimum legal fuel for a trip (generously sufficient in most cases anyway) and where appropriate we reduce ground delays by utilizing an intersection departure provided the figures work out.


PS, I've always heard that the 3 most useless thing to an aircraft are:

The runway behind you!

The sky above you!

And air in the gas tanks!


Chris  Smile
"Just a minute while I re-invent myself"
 
Mr Spaceman
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RE: What's This Airline Pilot Going To Do? - Takeoff?

Thu Jun 19, 2003 5:01 am

Hello M717.

Thanks for explaining that accelerate-stop distances are predicted on maximum anti-skid braking and spoiler deployment, but do not consider reverse thrust, and if any of these systems are inoperative, then there is a takeoff distance penalty.

So, I guess if a 767 pilot (for example) discovers that his ground spoilers are INOP while setting himself up for an approach, he simply pulls out a manual of published penalty distances, chooses the penalty that applys to the existing conditions (density altitude, wet/dry runway, rwy slope, etc, etc), and adds that distance to the calculated landing roll-out required. In this scenario, could the runway turn out to be to short, thus an alternate rwy or airport is needed ..... or is this highly unlikely?

Also, if the ground spoilers are INOP prior to departure, and a distance penalty can be used, does this mean the spoilers are on the aircraft's MEL list and can be deferred?


Chris  Smile
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m717
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RE: What's This Airline Pilot Going To Do? - Takeoff?

Thu Jun 19, 2003 5:21 am

In the approach scenario you used, it most likely would not be apparent that the ground spoilers were inoperative until they didn't/wouldn't deploy upon landing. Now, it might be evident that the automatic function of the ground spoilers might be inoperative, but in that case, you would simply manually deploy the spoilers.

As far as the MEL goes, every aircraft type has it's own MMEL (Master Minimum Equipment List); then each operator has it's specific MEL. But, to answer the question as you posed it...Yes. If the ground spoilers are INOP prior to departure, and a penalty applied; then the spoilers would have to be on the aircraft's MEL, and that would be noted on the dispatch/flight release, along with the applicable performance penalty. (Usually, this penalty would be in the form of a reduction in the maximum allowable takeoff weight.)

[Edited 2003-06-18 22:22:39]
 
Mr Spaceman
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RE: What's This Airline Pilot Going To Do? - Takeoff?

Thu Jun 19, 2003 6:03 am

Hello M717.

Thanks for your reply.

OK, so every aircraft type has it's own MMEL as well as it's operator's specific MEL. I don't believe I've ever heard of the MMEL before (but I'm probably wrong  Wow!). I suspect the operator's MEL is less flexible with regards to what systems, etc, are allowed to be INOP before dispatch releases a flight.

Oh No! More questions! When will it ever end????  Nuts

How does an airline resolve a performance penalty (because of the anti-skid system or spoilers being INOP) by means of a reduction in the maximum takeoff weight? Do they remove fuel, bump passengers, or simply place some baggage / cargo on another flight?

This method sounds like it could be a real hassle. Especially if the problem doesn't occur untill after the aircraft is loaded (or is already taxiing fromit's gate). In such a situation, would an airline consider adding to the takeoff distance required to reach V1 or even using full power instead of derated thrust? This would help to save time.

Your explanation about the pilots being warned that the spoilers won't arm while airborne makes good sense.

Chris  Smile

"Just a minute while I re-invent myself"
 
m717
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RE: What's This Airline Pilot Going To Do? - Takeoff?

Thu Jun 19, 2003 11:20 pm

Chris,

I should clarify about the takeoff weight penalty. First, the max allowable takeoff weight is limited by the lower of the structural limit, the runway limit, the climb limit (which could be limited by the second segment climb gradient or an obstacle), the brake energy limit, or the takeoff wt can be limited by a landing wt limit, such as the max structural landing wt, landing climb limit, etc.

The weight penalty that would be applied for an inoperative anti-skid or spoilers would be applied only to the runway limit weight. This may or may not be the ultimate limiting factor. For example, at my airline and on our route structure (short-medium stage lengths, mostly low elevation airports with long runways, etc.), we are almost always limited by our max landing weight, so applying this weight penalty to the runway limit does not affect our maximum allowable takeoff weight, but may have an impact whether or not we can do a reduced power takeoff, and if so, what kind of reduction we might be able to take.

To answer your question, obviously, if this is known ahead of time, then a certain amount of planning can be applied. The first area we might look at if we needed to reduce our planned takeoff weight would be the fuel. Many times we take extra fuel for contingencies, or perhaps tanker fuel due to price differences at various stations. You could consider child weights (if applicable) when figuring the pax weight. If additional reductions are needed, the next place you might look would be at non-critical cargo. Next would probably be non-rev and stand-by passengers and bags. And finally, you would have to start bumping revenue pax, bags and cargo.

Even if it were a last minute deal after everything was loaded, the first place to look would be the performance numbers to see if the new runway limit weight would be the limiting factor. If not, then press on. If so, then perhaps there is a longer runway available than what was originally planned, or perhaps you had planned a reduced power takeoff, so you would then check the limits for a max power takeoff, etc. If there is simply no way to make your current weight work, then you would have to reduce your weight as described above by whatever method would be most effective and least disruptive. Those decisions are made jointly by the Captain, the dispatcher, and the operations personnel.
 
Mr Spaceman
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RE: What's This Airline Pilot Going To Do? - Takeoff?

Fri Jun 20, 2003 3:49 am

Hi guys.

> M717, Thanks for explaining in detail that an aircraft's Maximum Allowable Weight is comprised of several different weights and limits, and that any of these can be affected when a weight penalty is imposed .... depending on the circumstances.

Also, Thanks for explaining the various options that an airline operator has to choose from when deciding how to conform to a weight penalty, especially when an aircraft's physical weight needs to be reduced, and that the most effective and least disruptive method used is a decision that's jointly made by the Captain, dispatcher, and operations personnel.

I find this kind of info very interesting. Big grin

In this photo of a 737-3's cockpit, you can see that the calculated V speeds are .....

V1 - 139
Vr - 140
V2 - 147

Unfortunately, I can't make out what the other numbers are for. Sad Also, I'm wondering why the pilots have this Takeoff Data document out in view when they're flying at 35,000 feet. Do they still need it?


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Here's a tidbit of info I read in a magazine today about Vr speeds.

Vmu (minimum speed the aircraft will lift off the runway - unstick speed), is a factor that must be considered when normal takeoff airspeeds are calculated. The published takeoff rotation airspeed, even with a very aggressive pitch up, must be at least 110 percent of Vmu.

Chris  Smile
"Just a minute while I re-invent myself"
 
liamksa
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RE: What's This Airline Pilot Going To Do? - Takeoff?

Fri Jun 20, 2003 4:38 pm

Here in OZ i believe it's:-

Vlof ≥ 1.1Vmu for all engines operating (lift-off speed as opposed to rotate speed)

Vlof ≥ 1.05Vmu when critical engine inop

Rob.

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