Hi all,

I post this question here as it is not a PMDG problem, but rather TOPER issue. I have also posted the question on TOPER's forums but wanted to ask also here as the audience is bigger.

I face a problem with TOPER for the 777-200LR. As you can see in the picture, TOPER advises to use an assumed temperature of 70C but the V speeds are in complete disagreement with PMDG's calculation. I have also put TOPCAT in the picture, where it suggests 50C instead and its V speeds are much closer to the PMDG. If I select 50C in the FMC, then the V speeds of TOPCAT match PMDG's agree precisely..

So, my question is why TOPER is giving wrong V speeds and more assumed temperature? Is this a bug? Or just means that TOPCAT is better?

Edited March 6, 20188 yr by Daedalus

Get the books out and calculate it by hand and compare. 

TOPER and TOPCAT provide two different results, everytime, because they are calculating two different things.  TOPER ignores obstruction clearances and performance limits, TOPCAT includes this data in the calculations.  As for the differences between FMS and TOPER just keep in mind that PMDG uses Boeing data licensed to them by Boeing whereas TOPER is based on data from hobbyists and usually obtained from 3d parties.  The only time I use TOPER is for my PMDG NGX in the B736 variant, where I only apply flex and not derate.

Thanks for the reply @downscc . So, it seems what you say is that TOPCAT and of course PMDG is more accurate. Agreed, the problem is that TOPCAT is abandoned by the developer and there are types that it does not cover, where TOPER does, so for me TOPER is very useful. I'll just have to take its calculations with a margin of error I guess, and I'll try to press the developer to fix these inaccuracies. 

TOPCAT is a fantastic product. Don't know why it was abandoned. The fact it works in combination with PFPX is an added plus.