Airbus EFB T.O Performance
 

Hi guys, is anyone here familiar with the concept the Airbus fly smart EFB uses in calculating takeoff performance? In particular I'd like to ask about the stop margin figures. When we are runway length limited, we often get stop margins in the region of a couple of meters, the lowest I've seen is 2m.

It does bring some uneasiness when we see that simply because it's too close for general comfort. Does the calculation take into account stopways (if there is for that runway), or does it always assume a balanced field? Do you guys try to increase the stop margin when presented with figures like this or do you take it as it is?

My employer recently introduced EFB's including the use of flysmart for performance calculations. A number of our Crew seem to have the same concerns as yourself. I think you need to remember that the accelerate stop distance part of the take off calculation ensures the maximum weight that allows to accelerate to v1 then stop ( I.e Margin being 0m ). So when compared to using paper charts for take off performance, we don't have access to stop margin information ( I always assumed it to be 0m anyway ), now we can see a figure some people are uncomfortable with it.

Personally I don't make any adjustment to the runway dimensions to increase the stop margin, but some people do.

Another thing to consider is that if you use FLEX, the performance calculation assumes the Flex temp as OAT. E.g. if your FLEX is 65, then the performance is calculated as if it was really 65 deg outside. This greatly affects TAS (and hence GS) calculation.

If your actual temperature is less then flex (and it generally is), your actual TAS at V1 will be much less (like 10 knots) than the calculate. You will therefore need less runway to accelerate and decelerate in case of RTO.

As a result, your actual stop margin is significantly higher than the calculation (~1000ft in typical conditions). Bottom line - no need to worry about stop margin, even if the software shows 0

We use the fly smart in daily ops . Even if the margin is 1 mtr it's good enough as the calculation do not take credit for reverser , and in case of a reject takeoff the aircraft stops with a good margin to spare. The result through fly smart is also a bit conservative though it looks optimised..It has some margins built within.

As stated above, the stop margin displayed assumes that the OAT is at the flex temp. Your actual accel-stop distance will be 3% less for every 10 degrees of difference due to the difference in TAS.

Eg. ASD displayed is 2300m. Flex of 60 degrees and OAT is 20 degrees.

Actual ASD is 12% less ((60-20)/10 x 3%) so really it's 2054m giving you an extra 276m to play with.

It will if it's wet!

In our outfit most of the crews do one of two things when the stopmargin is only a few meters: either use "runway shortening from the beginning", or raise your take-off mass by 500kg.

Yes, MDr. That's exactly why on the PC software there is an option NOT to display the ASDA margin. To prevent pilots from abusing the engines when they think they are being smart.

In all fairness, it DOES come down to how much money / time / resources are companies willing to invest into proper crew training.

Whilst I calculate differently from EGPFflyer, there is empirical FDM data to prove his numbers are comfortably accurate.

The 3% per 10 degrees is in our Ops Manual. I'll see if I can dig out an airbus reference

We started using EFB over a year ago. Within weeks on the line I found FO's proposing all sorts of homespun ideas on how to increase the stop margin when they felt it necessary. These were often not their own ideas, but methods they'd been shown by other Captains.
Personally I think it is dangerous and deluded to play around with the data inputs (altering TOW?! altering RWY length!?) without a specific policy or procedure published by your company. You might THINK your modifications are reasonable and even conservative - but think about the consequences of any kind of incident where an RTO goes even slightly wrong. Your 'massaging' of the EFB figures is going to be used to hang you out to dry. You will carry the blame for the incident/accident. Do not do it. If your company has a recognised policy which might improve the Stop Margin, use it. Perhaps an intersection TO calculation is allowed. That will legally allow you to improve the Stop Margin figure.

This issue is most likely to be a problem when doing FLEX TO's of course. The EFB will seek to acheive MAX FLEX TEMP and this can mean even a low weight takeoff on a long runway showing minimal stop margins. The EFB software does have an option to choose a REDUCED FLEX Temp. That would be the ideal solution. It is what we used to do when we had paper tables - Airbus published a procedure allowing the Commander to drop the FLEX TEMP down to a lower value if he felt the need. In my company they have not activated this EFB option - meaning, they have taken away my ability to reduce the FLEX if I felt the need. In my opinion this is a retrograde policy and one which further erodes the Commanders right to exercise Airmanship and Command decision making. When I asked them why they did so they told me they think it would only 'confuse' pilots!
The REAL reason is - they don't want you to reduce the FLEX temp, for economic reasons (somebody above charecterised this as 'not trashing the engines! Bull.). Its all about the $$$.
Unfortunately it leaves me with only two options. I can choose only MAX FLEX, or TOGA. Which ultimately costs them more $$$.

I've heard this argument in my company too. "You're only worried about stop margins now because now you can actually SEE the stop margin, when before you couldn't!".

Two things about that argument; First - having been in this business for decades and on multiple types, in all sorts of weather conditions, and on all lengths of runways, I think I have a fair idea about the RTO risks I might face on a short runway with high WAT conditions. Call it 'experience', call it 'intuition', whatever you like - but I'm not dumb enough to be suckered into believing it carries the same risk as a 10'000ft runway in low weight and perfect ISA conditions. I don't need a pretty picture on an EFB to tell me to consider a lower FLEX Temp, or even TOGA.
Second - when I went on the Airbus I got a new system called EGPWS with a nice picture on a TV display. I already knew where the terrain was - I briefed that from my charts, including highest spot heights, terrain location relative to my SID/STAR, highest Sector MSA's etc. But now I have it all right there in living colour on my ND. It enhances my already good situational awareness. I'm glad to have it.
Likewise with the EFB. I always knew the threats, and how I could mitigate them. The EFB gives me even greater situational awaeness, thus improving my safety margins.
Should I turn off the EGPWS picture if it interferes with the $$$ imperatives?
Should I turn off the EFB stop margin display if it interferes with the $$$ imperatives?
It seems some already do!
Disgusting.

You still manually program the thrust and speeds, right? Just take the optimum FLEX that the EFB spits out, drop 10 degrees, and use that for takeoff.

The airbus iPad EFB shows us all possible flex temperatures. I have never seen someone massage the numbers, but quite often we take a degree, or two, lower flex temperatures to get the margin we like. As the company leased the engines on average thrust reduction we are fine, as we easily achieve that anyway. Why do pilots reduce flex and increase margin? Well, we had a runway overrun a few years back, where even a sizeable margin was of no use although the take off abort was done according to OEM procedure and well within limits, since then pilots often feel uncomfortable to use every last inch.

EFB software is not new to us though, we have been using EFBs for more than 15 years now, airlines somewhat new to this might react differently.

Denti - our company does not give us the option to see or select from a list of FLEX Temps. Its MAX FLEX or TOGA. This is done purely for financial reasons. They are in the habit of phoning crews who used TOGA and asking them for an explanation. Its intimidation, and it works on many, hence the 'trickster' attempts at getting around the numbers (hello callmeJB).

Your story about the overrun is instructive.
Yes there are lots of margins added to our Performance calculations, but always remember that the base data is derived from test aircraft, perfectly maintained by the manufacturer, with new brakes, on a standardised runway surface, with a test pilot at the controls who is pre-warned and prepared for the RTO.
Ordinary sods don't have all those advantages.
Step outside the ideal world of razor sharp decision making and reactions and your 'additional margins' start eroding.

RB: RTO test specification requires brake pads worn down to 25% or less. Please check your signal/noise setting.

On the other hand, I liked the "show flex table" option too. In case you had reasons to dispute the MAX FLEX data, it provided for a chance to do things right.

What I miss sorely since the paper days, is the option to "move towards left (tailwind columns) to obtain lower speed for the same FLEX". The EFB core module optimizes to the max, pushing V2 and V1 unnecesarrily high. I do not see the option of 4,6% OEI gradient against 3,8% at a shoreline airport as a benefit, if the steeper ask for 153 V1 compared to the latter's 140 kts.

Denti: Is there a publicly available report on that, sounds quite important!?

Sounds like your problem is the company CP and bean counters, not the pilots and EFB.

I can't see any reason to not give the full range of figures. Crew can still get a please explain, but have more choice to choose something appropriate rather than the extremes.

Tell me about it.... :(

Is that so....seems strange to add margins onto an already decremented brake system. But anyhow, I'm not a test pilot. Just an average Joe Soap. I have to make allowances for my shortcomings.

I think the elefant is the achieved braking action, there are allowances for us Joes capability.

I just googled a 737 slip off in Dortmund around 2010, even the picture on AV Herald tells a story.

I have seen a number of colleagues of mine start getting jittery with such a low stop margin. To add to the points already discussed here, there are a couple of other safety factors inherently built into the EFB computation.

1. EFB assumes 50% of the headwind and 150% of the tailwind for take off performance computation.
2. EFB assumes Reversers to be inoperative for dry runways..

Factoring in these conservative assumptions the actual stop distance would be less than the one indicated in the EFB so the stop margin would be a lot more than the calculated figure

To add on to my previous narrative, in case someone is actually worried about the stop margin, there is a simple work around through the whole procedure. Reduce the runway length at the end by about the Stop margin distance (say 100m) that you'd ideally like to have anyway and compute the performance. This will give you a significant stop margin in actual conditions.

Select TOGA, or calculate the performance from an intersection whilst taking off full length, reduce runway length, enter a tail wind...there are many many ways to increase your margins. But why bother? You know what performance is based on and use that knowledge. Otherwhise stay in bed.

Or use TOGA+flap3 all the time!
The only time I seriously consider lowering the Flex and the speeds is in LVP's, for very obvious reasons.

In more than a decade using the software I have only seen one absolutely limiting takeoff, i.e. TOGA, F3 and close to zero margin.

Guys thanks for the discussion.

Is there anywhere at all we can get a copy of any document that explains what logic does the EFB calcuLates its figures on? Like he no reverser credit on dry runways.

Getting to grips with A/C performance would be a good start, then Airbus PPM.

Interesting topic. In addition to all your assumptions, the line up distance used to offset Nose Wheel and MLG are important. Perhaps educating the end user too.

For dry assumptions, yes, the reverses are not considered, however, if your stop Margin shows 2m, that’s assuming the stopping action took place at V1 plus 2 sec reaction time. Decelerating is now with 50% of the referrers that you have anyway. (Practically speaking). Therefore the Stop margin is brought quite a way forward and will always look different from the computation versus the real thing. That’s what and how we try to educate our guys.

Also someone has mentioned before, the assumptions are based on an avaerge call to stop, cold and work brakes.

Wind components assumed for the calculation at this of 50 or 150% depending if it’s head or tail. Again very conservatively put, additional margins are built into the assumptions.

Your EFB administrator can set up the output of the performance module to display a range of Flex temps and or TOGA. However, you’re now not using the optimisation process ‘as advertised’

EFB
 

Can aircraft movement be seen in EFB. Can the crew use EFB for identifying Runway so that take off incident on unassigned Runway or Taxiway can be avoided. There had been many such incidents in the world.

The requirements set out for the calculation of take off performance are regulatory and should be contained in your company OMB and aircraft FCOM.

With TMAXFLEX you are calculating the maximum theoretical outside temperature for which a takeoff can be safely achieved and reducing the thrust output accordingly. If you're unable to alter that value, you can artificially alter the environment to create conditions which favour higher thrust.

Personally I have not reduced runway length to do so, however I frequently factor in a nil headwind or slight tailwind in order to "worst case" things. I've found even a slight tailwind has a significant impact on the takeoff performance, given the factorisation.

In addition we regularly use intersection departure calculations even when departing from full length.
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We just got this feature this year. It's not supposed to be the primary way to identify runways or taxiways but it's a great tool for situational awareness

Yes you can do it, but the position depicted can be off by quite some feet depending on the GPS signal quality received on the EFB. The Airbus' SOP for this is identify runway and intersection on the lining up checklist. Inserting a TO shift at the PERF page also helps to raise awareness, and yes before somebody notes, I know that with GPS HIGH inserting a TO shift is not necessary, I am just pointing out that seeing a number there before lining up makes you remember that you are doing an intersecting departure and the numbers are for that case. Compare this number with the runway left behind and reassure yourselves the numbers look right.

I've seen many people tweaking the EFB to make the remaining distance to something they like more. I am not very in to this procedure but I can understand their fears.

Depends on the system, ours get the FMCG Position via an in-cockpit WiFi link. Again, it is not supposed to be the primary means og navigation, but helps a lot, especially on unfamiliar airports and with automatic chart switching and zooming.

thanks. It will be of great help.

I think the best way to identify the runway is by looking ahead through the front window rather being distracted looking to the side at an iPad.

Mind you, I get annoyed when people are looking at their phone when walking down the sidewalk or driving rather than looking where they are going.

This shows a general lack of understanding of aircraft performance and Airbus FlySmart calculations. You should ask your Tech Pilot for a briefing to correct this. You are achieving absolutely nothing by those small adjustments.

Maximum engine wear saving is achieved by the first few degrees of Flex. That benefit is lost with ‘creative accounting’.

The accelerate-stop distance on a dry runway is the greater of the following values:

a) ASDN-1 dry = Sum of the distances necessary to:
- Accelerate the airplane with all engines operating to VEF
,- Accelerate from VEF to V1 (1) assuming the critical engine fails at VEF and the pilot takes the first action to reject the takeoff at V1
- Come to a full stop (2,3)
- Plus a distance equivalent to 2 seconds at constant V1 speed

1 Delay between VEF and V1 = 1 second
2 ASD must be established with the “wheel brakes at the fully worn limit of their allowable wear range” [JAR/FAR 25.101]
3 ASD shall not be determined with reverse thrust on a dry runway

b) ASDN dry = Sum of the distances necessary to:
- Accelerate the airplane with all engines operating to V1
, assuming the pilot takes the first action to reject the takeoff at V1
- With all engines still operating come to a full stop
- Plus a distance equivalent to 2 seconds at constant V1 speed

ASDdry = max of {ASDN-1 dry, ASDN dry}

The accelerate-stop distance on a wet runway is the greater of the following values:

• ASDdry • ASDN-1 wet = same definition as ASDN-1 dry except the runway is wet1
• ASDN wet = same definition as ASDN dry except the runway is wet

ASDwet = max of {ASDdry, ASDN-1 wet, ASDN wet}

Influence of V1 on Accelerate-Go/Stop Distances

For a given takeoff weight, any increase in V1 leads to a reduction in both TODN-1 and TORN-1. The reason is that the all engine acceleration phase is longer with a higher V1 speed, and, consequently, in case of an engine failure occurring at VEF, the same V2 speed can be achieved at 35 feet at a shorter distance.

On the other hand, TODN and TORN are independent of V1 as there is no engine failure, and thus no consequence on the acceleration phase and the necessary distance to reach 35 feet.

On the contrary, for a given takeoff weight, any increase in V1 leads to an increase in both the ASDN-1 and ASDN. Indeed, with a higher V1 speed, the acceleration segment from brake release to V1 is longer, the deceleration segment from V1 to the complete stop is longer,

and the 2 second segment at constant V1 speed is longer.

It is observed that Pilot monitoring (PM) is generally very busy in EFB for checks (head down) and misses visual clues to lineup on correct RWY. So if Pilot flying (PF) makes error there is no defense available as PM is head down. So i assume checking position on EFB might be useful. What are your suggestion.