Is it a common airline practice to base T/O speeds on the actual T/O weight when an assumed temp thrust is used?

Let's say the current outside air temp is 15 C and you have decided to use 50 C as the today's assumed temperature for your takeoff. In this case, use of the T/O weight the assumed temp thrust supports gives you the balanced V1.

But our company rules are to use the T/O speeds of the "acutual" T/O weight instead of those that the T/O weight the assumed temp thrust applied provides. I assume this rule has been made to give a greater safety margin for a runway overrun in the event of a possible rejected takeoff at the expense of decreased obstacle clearance, since use of the actual takeoff weight invariably brings lower V1, Vr, and V2 speed than when the T/O weight of the assumed temp thrust is used. My question is: is it a common practice among commericial airlines to use the actual T/O weight instead of the assumed temp T/O weight?

• Assumed temperature is simply a way to reduce your thrust to some predictable amount that you can still find in the charts. I've never heard of using an assumed weight for 737 performance. Fictitiously adding weight reduces assumed climb performance, which serves no good purpose. Can you give an example of how much you see "assumed weight" differ from actual weight? – Ralph J Mar 1 '18 at 15:02
• Finding the weight (at whatever thrust setting you're using) that produces a balanced field isn't about "assuming" the airplane weighs that much, it's simply determining how heavy you could be to still meet all performance requirements. Base your takeoff & climb speeds on what you DO weigh + whatever thrust you ARE using (even if that thrust setting is being reduced based on an assumed temperature). No good comes from using a low V1 and high VR with a light jet & long runway just because that's the V1 & VR that you'd have with 40,000# more weight! – Ralph J Mar 1 '18 at 15:11
• In my understanding the idea of the assumed temperature method is to calculate the whole takeoff as if it was as hot as you‘re assuming. That gives some margin on the day due to the true airspeed (and thus distance covered in a given time) being a bit lower than assumed. Mixing normal temperature speeds into it, especially V1, might not be conservative (I‘d have to think about it a bit more!). The only exception are VMCG and VMCA which have to be calculated at actual temperature, obviously. By the way, whether it’s a common practice or not won’t be easy to answer - only whether it’s safe. – Cpt Reynolds Mar 1 '18 at 21:01
• @Cpt Reynolds "Mixing normal temperature speeds into it, especially V1, might not be conservative." At the balanced V1, the accelerate-stop distance and accelerate-go distance equal to each other. As the V1 decreases from the balanced V1, you need a less accelerate-stop distance, while you need a greater accelerate-go distance. Granted that's the case, doesn't a lower V1 always give a greater safety margin at least in terms of an overrun in the event of a reject takeoff? – lemonincider Mar 3 '18 at 8:34
• @lemonincider Yes indeed. I would in that case be concerned about the accelerate-go case, where the aircraft has to complete the engine-out takeoff from lower speed than the balanced full-thrust V1, but only using reduced thrust. As I said, it’s entirely possible that’s OK, but it doesn’t feel right to me. I would have to think about it some more before being certain. – Cpt Reynolds Mar 3 '18 at 11:47