Having issues with the way the EFB calculates t/o performance.   I'm finding multiple cases where it simply tells me it can't calculate the TO numbers and I need to reduce weight, change flaps setting, etc.    In nearly every case, I've not been close to GW and have had favorable wind / temp conditions.  Today I was at KMDW with 160PAX, 6K of cargo and a Simbrief calculated fuel load of 16,200 lbs and ZFW of 137.2K lbs.   Had favorable winds.   Tried to run the numbers for TO-1.   Got the message.   Went to TO settings, same.   Tried Flaps 10, same.   Finally I had to drop the PAX numbers down to 70 and the EFB finally calculated my V-speeds.    I ended up just adding 10 knots to each of the V numbers when I programmed the FMC.   Takeoff went fine (with AC packs on), I hit VR with plenty of runway left.    I don't get it, I know Midway has shorter runways but I don't see any reason why a RL MAX-8 in similar conditions would be unable to take off from 4R. 

This happens quite often, usually when I've got a heavy fuel load.   I had a flight from KBOS to KSFO, using 4R (10,000' runway), again with favorable weather conditions and a less than full pax / cargo load.   Same thing.  Hate to think what will happen if I want to do a max-range flight, I'll probably have to tell the EFB I've only got 4 passengers on board to get it to cooperate.   Anyone else having issues like this? 

Same issue for me. I keep trying this aircraft and then going back to PMDG….simbrief will calculate suitable numbers incl a derate with all the same weights/weather etc. 

1 hour ago, 11bee said:

Having issues with the way the EFB calculates t/o performance.   I'm finding multiple cases where it simply tells me it can't calculate the TO numbers and I need to reduce weight, change flaps setting, etc.    In nearly every case, I've not been close to GW and have had favorable wind / temp conditions.  Today I was at KMDW with 160PAX, 6K of cargo and a Simbrief calculated fuel load of 16,200 lbs and ZFW of 137.2K lbs.   Had favorable winds.   Tried to run the numbers for TO-1.   Got the message.   Went to TO settings, same.   Tried Flaps 10, same.   Finally I had to drop the PAX numbers down to 70 and the EFB finally calculated my V-speeds.    I ended up just adding 10 knots to each of the V numbers when I programmed the FMC.   Takeoff went fine (with AC packs on), I hit VR with plenty of runway left.    I don't get it, I know Midway has shorter runways but I don't see any reason why a RL MAX-8 in similar conditions would be unable to take off from 4R. 

This happens quite often, usually when I've got a heavy fuel load.   I had a flight from KBOS to KSFO, using 4R (10,000' runway), again with favorable weather conditions and a less than full pax / cargo load.   Same thing.  Hate to think what will happen if I want to do a max-range flight, I'll probably have to tell the EFB I've only got 4 passengers on board to get it to cooperate.   Anyone else having issues like this? 

I've been using Simbrief's performance calculator and been happy with it. Give that a try, not like the iFly tablet is convenient or easy to use anyway 😄

4 hours ago, ianb2469 said:

Same issue for me. I keep trying this aircraft and then going back to PMDG….simbrief will calculate suitable numbers incl a derate with all the same weights/weather etc. 

I got fed up with some of the bugs that probably will never get fixed in the iFly, and went back to the PMDG 737-800

Interesting. I thought I was in the minority as so many speak so highly of the iFly, but I’ve also left her in the hangar and gone back to PMDG. 

If you only tried flaps 10, you had some performance left on the table.  Flaps 15 or 25, TO, bleeds off if necessary.

That said, no takeoff perf calculator in the simulator bears much resemblance to the real world.  They're just trying to return plausible numbers.  Obviously, things like balanced field length, second segment climb, IC V speeds etc aren't being looked at.  Because if they were, you'd have the real life takeoff calculator.  Which costs thousands of dollars for obvious reasons. 

I don't bother with performance calculations in the game for this reason.  They aren't real anyway, in any developer's product.  I'd say try various calculators until you get some numbers you like, if you don't want to just use what you know will probably work.

2 hours ago, Stearmandriver said:

That said, no takeoff perf calculator in the simulator bears much resemblance to the real world. 

I guess you have not tried the "Virtual Performance Tool"?

The only one that isn't free.

Edited August 18, 2025Aug 18 by Farlis

18 minutes ago, Farlis said:

I guess you have not tried the "Virtual Performance Tool"?

The only one that isn't free.

I have.  What does it cost compared to an actual license to Dynamic Source, etc?  

Of course it doesn't calculate data the way that a real world tool would.  It's just formatted to look like it does.  These aren't simple solutions, especially when every bit of payload must be squeezed out of them. 

I get why one wants to use a performance tool in the name of immersion.  But it's kind of like someone on here a few days ago wanting to know why Simbrief was reporting that a Max 8 didn't have the range to fly a route that is in fact flown in reality by a Max 8 - because Simbrief isn't actually a real dispatch tool.  It's calculating solutions that seem plausible enough to be enjoyable in the game, but if it were really doing what real dispatch tools do, it wouldn't cost $8 / mo.  😉

1 hour ago, Stearmandriver said:

What does it cost compared to an actual license to Dynamic Source, etc?  

Professional solutions are ALWAYS way more expensive. Not because the data is more accurate but simply because the proprietor is milking the user for money. Kind of a "You use this in an environment that makes you money? We want some share of that. Give us more!"- Situation.

 

Take a simple Windows installation, or look at the way Lockheed Martin priced P3D for various uses. The programs remain the same, but the fees you have to pay for it are simply more expensive.

What do Airlines pay for charts? A multitude of what we simmers pay for the LIDO package (which is included and up to date in the sim) or via the Navigraph subscription.

They are the exact same package, and the disclaimer not to use them for real world naviagation is only there to cover all legal bases, not because they actually are of lesser quality or outdated. 

 

So I'm not sure there is that much of a difference in the calculations.

Edited August 18, 2025Aug 18 by Farlis

12 hours ago, Farlis said:

Professional solutions are ALWAYS way more expensive. Not because the data is more accurate but simply because the proprietor is milking the user for money. Kind of a "You use this in an environment that makes you money? We want some share of that. Give us more!"- Situation.

 

Take a simple Windows installation, or look at the way Lockheed Martin priced P3D for various uses. The programs remain the same, but the fees you have to pay for it are simply more expensive.

What do Airlines pay for charts? A multitude of what we simmers pay for the LIDO package (which is included and up to date in the sim) or via the Navigraph subscription.

They are the exact same package, and the disclaimer not to use them for real world naviagation is only there to cover all legal bases, not because they actually are of lesser quality or outdated. 

 

So I'm not sure there is that much of a difference in the calculations.

I think that legal liability and certification costs would explain more of the difference than outright money-grubbing, but also, there is a large difference in the calculations. 

The tools for the game aren't nearly as fine-grained as real-world, safety critical calculations.  This is probably partly because the aerodynamics themselves aren't as accurate, but also my guess is that these perf calculators just include data for a few basic conditions, and deeply interpolate between them.  And I mean, why would you do anything more complicated?  The data you're producing is consequenceless.

I'm sure I'm not the only one who likes to test out performance calculators.  When I get a new airliner, I like to load up on a short field on a warm day and then play with weight until I find the max weight at which a performance critical solution can be returned.  Then I try a V1 cut, and see if I can stop, and if I can go.  I've done this with the built in tools on the PMDG 73s in multiple sims, on the Fenix, the PMDG triple, the iFly, and multiple aircraft using the old Topcat, the Simbrief numbers, VPT and others I'm probably forgetting.

I'd say it works about half the time.  Often, I either can't stop, or can't go.  This isn't really a surprise.  Obviously, one hopes the real-world data is performing a little better.  😉

Personally, I'd agree that the iFly calculations err on the side of being conservative.  Also though, I think simmers forget that takeoff data is always calculated assuming an engine failure a V1.  Thus, on any takeoff where you don't have an engine failure, you have over twice the performance available from V1 onwards as your takeoff data was expecting.  (Twice the thrust and less drag, compared to the scenario your data was calculated for.)

Unless you're practicing V1 cut scenarios, there is no takeoff where runway length or obstacle clearance should feel tight.

 

12 hours ago, Farlis said:

What do Airlines pay for charts? A multitude of what we simmers pay for the LIDO package (which is included and up to date in the sim) or via the Navigraph subscription.

Airlines pay for tailored chart production, and for a controlled data source for certification purposes.  They *may* also pay for performance engineers to actually create tailored procedures and get them certified, or they may do that bit internally.  But they're certainly paying for more than we are in the sim, which is a simple display.

6 minutes ago, Stearmandriver said:

and for a controlled data source for certification purposes. 

Exactly. It's just a question of legality, not a question of quality.

53 minutes ago, Farlis said:

Exactly. It's just a question of legality, not a question of quality.

Well, it's both.  Doing it this way is legal, precisely because there's built-in quality control.