Should I take the longer runway
 

You are at an airport with two parallel runways operating a jet airliner. A shorter one and a longer one by perhaps a couple of thousand feet. Both are available for departure. The taxi distance to the shorter one is a couple of minutes shorter.

The aircraft is near max takeoff weight and the takeoff performance calculation shows that at the takeoff weight for the aircraft, the short one is acceptable but it is right at the limiting weight for the runway length using full takeoff thrust.

So it is decided to use the longer runway. The only thing is that with the longer runway a derate and ATM thrust reduction is used for the takeoff along with a different flap setting.

Without including a bunch of variables such as the longer runway covers weather changes, payload adjustments, etc.......How much advantage have you gained by using the longer runway. Is the reduced thrust takeoff negating most or all of the advantage that the longer runway offers?

Good quesiton, JammedStab. I guess you have gained an advantage of not having to use max thrust for takeoff. Maybe not a big deal on the 744, but on the 742 with the worn out Pratts it was something to avoid, if possible. Since ATM is used on the longer runway instead of a straight derrate (TO 1, TO 2), then you could still push the power up on the rest if you lost an engine. Plus, if you are over guarantee you get more time taxiing to the longer runway. Would management call you on it?

Thanks. Just a performance question so cost in not a consideration.

You seem to think that a reduced thrust takeoff is a bad thing?

The reduced thrust means that all other things being equal, you're probably more controllable in the event of an engine failure. (Although both cases meet minimum certification standards, the manner in which they do so may differ)

Reducing the take off thrust reduces the 'wear' on an engine, hence cost.

Assuming that you meet all performance requirements and any additional company requirements like a 15% margin on runway lengths, then either runway is acceptable. That is the point of doing the numbers. As for the economics, they have to be set in context. If you need the extra minutes to get to a closing airfield or an airborne slot, then the shorter runway is obvious choice. But if you are told "de-rate" any any cost, then it's the longer runway only. But if, like most of us here, you are not given the raw numbers you will have to make up your mind. If I'm on time, I would have prepared the numbers for both but I'd flip a coin to decide.


PM

No.
There is better overall aircraft performance than you may suspect due to the real OAT is colder than the assumed temperature input for the engines. The engines would produce the same thrust if operated at the assumed temperature, but the wing is flying in the denser air at the actual OAT.

Always work from the hearing backwards...

If you use a performance computer to calculate takeoff performance, it is VERY likely V1 will be increased significantly on the longer runway, and the stop margin will not increase significantly.

In cases such as you describe, I often run several calculations, with and without derates and ATM reductions. I look for a good balance between thrust required, V1, and stop margin.

Also, I will ask for the longer runway when near the performance limits on the short runway.

Depends on performance software i guess. The airbus thingy throws out the highest reduction possible, right down to a 1m margin left on the runway. However, it also provides all lower flex temperatures and runway remaining margins for those figures, so take the one with the margin you personally are happy with.

That said, the company wants us to use reduced thrust as much as possible, so if there is no operational downside i would take in that situation the longer runway, reduce thrust a bit and use a larger margin.

Good answer and a good point by GRivet.

I don't think you will ever get a clear answer to this question. A longer runway has a higher flex, which lowers maintenance. But if the extra fuel burnt to get to that runway is excessive, than who are we kidding'? If your company's beancounters does not provide specific guidance, then they probably don't care either way.

As far as safety is concerned, as long as the numbers are correct, it should not matter to take the shorter runway. Not even at the hearing afterwards.

I agree with PENKO.

Many of us operate from a large selection of airfields in a variety of conditions. Unless they are particularly adverse (contamination, etc.) if the numbers work out then the quickest and easiest makes sense.

In some aircraft that use fixed derates as well as ATM I think I’d rather take the short runway and get some OEI performance!

I would compare the stop margins and use the plan that gives me the most wiggle room. As one gent said" always work from the hearing backwards".
Could you use the shorter runway? maybe yes, but is it wise, when there is a better solution.

We often had this at LAX. 24L vs 25R. 95%+ of crews would take 24L if it fit even if pushing right up on the numbers.

I would take 25R at LAX every time, but then we parked right next to it.

So, your question is
And then you have said to ignore cost.

So I'm not actually sure what "advantage" you are referring to. If you are referring to performance advantage in the case of an engine failure, the answer is what advantage? Either runway is safe in the case of an engine failure. One will have more thrust, so will be harder to control, but will climb better. The other will be easier to control but not climb as well, but will still clear terrain.

But, are you asking which runway is safer?

I would say the long one. For various reasons, as follows:

1. An engine is less likely to fail at lower thrust. I know many pilots feel better with more thrust, but all they are doing is increasing the likelihood of an engine failure. An engine at lower thrust will also suffer less damage from bird or foreign object ingestion.

2. On the longer runway ASDA for an RTO is less likely to be the limiting factor, so less braking may be required reducing the possibility of a brake/wheel fire or tyre deflation. Again, safety improvement.

3. What may conspire to kill you on the day may not actually be the certified standards of engine failure/stop/go scenarios. In fact, none of these should kill you because the aircraft is certified not to. What may kill you is a multiple failure, an error (eg thrust calculation error), a sticking brake, tyre failure, manipulation or handling error, or other event that is not possible to plan for. In that case, having more runway to sort it out may save you.

...or you may hit a dog crossing the runway whilst still slowly accelerating towards 155 knots VR when, on the shorter runway you would have been airborne ages ago with a VR of 129 and TOGA thrust.

..or your tire may fail catastrophically at those higher speeds on the longer runway.

..or you might inadvertently cross an active runway whilst taking a detour to the longer runway.

..or that careless buss driver slams into your right wing whilst taking said detour.


It is almost a philosophical question, no clear cut answers :)

Now, that’s a reason I would have given and it seems obvious but is it actually true of modern (jet) engines? Are there any statistics available to back it up, genuine question? With many piston engines peak mechanical and thermal stress occurs at less than peak power (not that this has anything to do with turbines but it shows that the simple answer is not always the most correct).

With the software we use, adding runway length often results in a lower flap setting (increased speeds) and improved V2 (even more speed). As brake energy is proportional to speed squared, that can be quite significantly more in the event of an RTO.

Agreed. Although I would add that there are many examples of aircraft failing or nearly failing to get airborne from very long runways due to too much thrust reduction, which might not have happened if full thrust or thereabouts was expected to begin with off a much shorter strip.

Hi FullWings,
It makes perfect sense to me that if an engine will happily run for ever at MCT or less, then it must be considerably less stressed and hence less chance of a failure than one operating at full power (10 min limit).

Excellent! Please provide a link or reference to those accident reports.

Is that true Goldenrivett? Does higher thrust really equate a higher chance of failure? I am no expert in engines so correct my if I am wrong, but take for example the A320 series. Practically the same engine on the 318, 319, 320, 321, just rated at a higher thrust, so it seems. So is an engine on the A321, with it's higher thrust rating more likely to fail than an engine on a 318?

One would think that even at max TO thrust these engines are far far below their breaking point.

Question is not very realistic. Most airports will be using the shorter runway for landing and the long one for T/O.

From a performance perspective both runways are safe.

If I were to have that choice, I'd take the shorter, max thrust, runway all things being equal. But, and a significant but, were I going to hold for the short one for more than a minute or two, the time/cost advantage is gone so I would taxi for the long one. Take the short one if you get something back for it like reduced airframe time otherwise taxi a bit longer for what gives you better margins is my recommendation.

Hi PENKO,
No. It should have about the same reliability. The reason being, the higher thrust rated engine will be removed from service earlier. Hence the higher maintenance costs.


The CFM56-7B Turbofan Engine
"In 2007, CFM breathed new life into the CFM56-7B fleet by introducing the Tech Insertion production standard. Compared to the base CFM56-7B, this new configuration provides operators up to 1 percent better specific fuel consumption over the engine’s lifecycle, and between 5 and 15 percent lower maintenance costs (depending on the thrust rating) through enhanced durability.

If everything goes well, you have burnt the engines a little more for the short runway. But thats it, we all know its safe...

But if it doesn't, we all know where we would like to be. On the short runway, eng fails at V1 you don't have extra trust to put on (SOP's allowing of course). On the long one you do, your climb out (all things being equal) on the long one will be easier (less flaps generally mean a greater climb rate and the extra thrust you could put on means that gets even better).

But there is of course a flip side. If the engine fails before V1, you stop, right! So on the short one, things are a little tight but the low V1 combined with a short taxi distance means your brakes are pretty cool prior to V1 and have less work to do. On the long one, you've taxied further, the brakes start a little warmer and the V1 is higher so they have a *load* of work to stop you.

There are always flip sides to the coin - Slopey shoulder time...

Had this scenario occur a few times at KATL headed to OMDB. Tower would instruct us to taxi to 26L with the explanation that there would be a 20 minute, or more, delay for runway 27R due to traffic.

Although we were legal by the numbers for 26L we always, (at least my augmented crew), accepted the delay and requested the longer runway, 27R.

Even then, because of our weight, a lot of Captains would use one of the higher thrust options offered by our AWABS, and some would use full power regardless.

Some light reading for you guys....

Stopkotte, Jack. “Minimizing Costs While Maintaining Performance Margins, Part 1 — Lowering Costs and Improving Reliability.” GE Aircraft Engines, September 2003. (If you can find a copy....)

"When less is more" - Aerosafety World magazine

Statistically, utilising the minimum Perf A compliant takeoff thrust makes you 5x less likely to have an engine failure, along with significant cost savings in engine wear...

It makes sense, yes, but with the kind of monitoring we have now in 2016 the situation is close to being able to trade thrust for life (TBO). While your margins are still good, does the chance of an actual failure increase with increasing thrust or are you just bringing essential maintenance forward? I suppose only manufacturers/operators could tell you that definitively. Yes, I did read the linked article above but it didn’t really answer this particular question. Is it similar to scheduling the oil change every 10,000 miles in your car but actually having it at 5,000 because the computer thinks it’s time as you’ve been driving like a loony...?

In my airline we get the vast majority of our engine failures in the cruise - of course there’s much more cruising time than taking off but you’d have thought if an engine was on the way out, it’d have gone earlier when you were thrashing it to get away from the ground, rather than producing half the power or less in almost steady-state.

Here’s one: Emirates 407. Although the calculations were 100T off to begin with, it was the subsequent excessive derate that did for them. Once you’ve accepted that you’re doing a reduced thrust takeoff, long runway and all, there’s not an immediate trigger as to whether a certain level of reduction is too much as there are too many variables: mass, temperature, obstacles, etc.

And another: MK Airlines 1602. Shorter than above but still nearly 3000m TODA.

I’m sure there are many more, some probably known only to the FOQA departments of many of the World’s airlines...

That was quite an interesting reading. Thanks for pointing us to that article. It particularly explains what Derfred first said: engine life improves using flex/derate thus reducing likelihood to failure.

Personally, given the choice and all other things being equal, I'd take the longer runway. The aircraft is designed to fly safely out of the short or the long runway, but more concrete to get off the ground will always be more appealing to me, even if using flex. If the engine fails you still have more thrust to use (assuming you're using flex) even though the aircraft should meet OEI requirements just using flex. If you reject the takeoff, the performance calculations already have you covered; if you're not comfortable with the margin given by the highest flex, you can use one that's a bit more conservative. Plus, I reckon the couple of extra minutes of taxi will be far offset by the reduced wear using flex on the longer runway (even if the question was not considering economics)

I'm struggling to think of anywhere I operate to where you get a choice of runways for departure so, for me at least, the question is moot.

That is NOT what is written in the article.
I can only interpret the figures in that article as that fixed derates cater for lower maintenance cost, not 5x more likely engine failure. Sure, if you do not perform any maintenance then yes, the engine will fail sooner. But that is not how we operate.


It's not moot at all. Substitute 'a choice of runways' for 'a choice of intersections' and you have the same age-old discussion wether it is safe to depart from an intersection.

Airmanship and Risk Management
 

Interesting discussion. After reading all of this, where is the discussion about Airmanship? -and- Making a decision to select the runway that poses the least risk to your operation?

Sure, we can 'fit' the numbers to the runways but at the end of the day, experience should lead a crew to make a decision to select the runway that poses the least risk to the operation. Airmanship isn't taught. It comes with experience and the desire to weigh all of the facts before departure, then do the right thing.

As an accident investigator, we do not look for fault, but we do look for the reasons that events happen and all of the details that led up to the event. Ultimately we search for clues to help mitigate the problem from happening again.

To attend an accident site or serious incident site, take the measurements of the area and make a few calculations, sometimes becomes disturbing. If in this case, we determine that the length available of the long runway would have provided a different outcome, the questioning becomes one of: Could you explain why you elected to depart from the short runway knowing that the longer was available?

One cannot take back the actions and outcome of the past however; we can all learn from it and prepare ourselves in better ways with a new mindset.

In the end, Fuel left in the bowser and runway behind you is of no use to you.

Just my experience anyways.

Safe flight!

This is pure intimidation. You could ask the same question for just about every decision made in the flight deck. Could you explain why:
-you derated
-you flexed
-you took an intersection
-you loaded that extra tonne of cargo
-you flew a visual approach when there was an ILS available
-why you did not upload an extra tonne of fuel on a CAVOK day
-why you did not land yourself on said CAVOK day
-why you came out of bed in the first place

A nice but absolutely useless quote.
In commercial aviation you have a responsibility as a captain to operate as safely AND as efficiently as possible. As such the above quote is not applicable. As a pilot and as a captain, you weigh the risks and take a responsibly informed decision. It takes as much airmanship to depart from the longer runway as it takes to depart from the shorter one.

Yes, very easily. The performance calculation that we performed showed that we were able to depart safely from the shorter runway; if it hadn't, we wouldn't have attempted to depart from it.

I'm really not sure what point you're trying to make.

Nobody is fitting the numbers to runways. Again, we will only depart from a runway if the performance calculation shows it to be safe to do so. To give an example: In Barcelona, departures are from 25L with a TORA of around 2600m. 25R is available for "performance reasons" with a TORA of around 3300m. Taking your simplistic approach, we should always request 25R for departure, because it is the "least risk" option, even though the performance software shows that we can perfectly safely depart from 25L. Never mind the huge delays that would be incurred by requesting the non-standard runway for departure; it is "less risk" and therefore it would be poor airmanship to accept the shorter runway! I think that you're ignoring commercial realities.

As Penko has already said, part of the job of a captain is to operate efficiently, while still maintaining adequate safety margins. I could fill the wings and put the trip in the centre on all sectors I operate, demand the longest runway and take off with TOGA thrust on every departure, but that's not what the company is paying me to do. Therefore, I make sensible fuel decisions taking all relevant factors into account, and use the software provided to optimised performance.

You appear to be affored a lot more time than most of us. Several calculations?

I have to agree with what the other are saying. As a commercial pilot you operate with safety, punctuality and economy as factors to our decisions. The optimal decision for a flight using "the seemingly safest course of action" would be taking off with a plane full of fuel and no payload and only flying on CAVOK days, but that's no way to make money. Standards have been created to operate as safely as it's deemed possible in the myriad of scenarios we might find everyday. From a safety perspective, I reckon it's as safe to take the short or the long runway, so long as the numbers are okay and there aren't other overriding factors (weather, terrain, runway asphalt condition, etc). Otherwise I think the statement we would be giving is that it would be unsafe to operate out of any single runway airport which is shorter than the longer runway in the question we are discussing.

Having said that, and understanding that realistically you aren't always given the choice of which runway would like to depart from (or it's not operationally/economically sound to do so on every single flight), if I'm given the choice I'd take the longer runway just because I reckon it's giving me a bit more wiggle room, in a nutshell.

Easy enough if you use an EFB. Usually i run somewhere between two and 10 calculations each flight. Each one takes a few seconds.

Perf A calculations assume an engine loss of thrust at V1-Vr. What are the chances? When did it last happen? I might discuss that the stopping case is more critical than the go case on a limiting runway, but I wonder if that is behind the question. To those who say the longer runway I ask if they have ever/never taken an intersection? Consider you are approaching the hold, 2 a/c at the holding point and an acceptable intersection coming up with a close slot and immediate takeoff possible. Performance already done: what would you do?
Now consider the landing options. If the longer runway is always your choice for takeoff, what about if there is a choice for landing? How many take the short taxi after landing option? Assuming all other things equal, i.e. acceptable performance.
It's not quite so basic as "do you feel lucky, punk, well do you?" It's a little more science, skill & judgement.
PENKO asks all the relevant questions. It would be an interesting question & dilemma on your command upgrade final line check. I wonder what the TRE would conclude?
However, as an escape clause; if the runway was contaminated or a significant tailwind, or windshear a possibility, or...or...then I'd think again.

Interesting discussion.

I think one of the key points is the use of the word “safer”. Like others, I’m paid to manage a safe *and* efficient operation - complete safety would be to lock the hangar doors and throw away the key, so there has to be a compromise somewhere.

Compared with all the other dangers out there which need to be avoided, shunning runways that are demonstrably acceptable performance-wise gives such a minuscule improvement in overall safety that it’s debatable you could even calculate it. It’s almost the equivalent of a lucky rabbit’s foot or four-leafed clover in that you may feel much safer but the underlying reality is little changed.

Incorrect responses to windshear, GPWS, TCAS, UAS; the wrong flap setting, the wrong thrust reduction, the wrong MSA, the wrong runway. Not de-icing properly, not being proficient in unusual attitude recovery and so on... These are some of the biggies that can really spoil your day. Just thinking about the possibility of any of the above before you set off could increase “safety” by far more.