What's the rule of thumb when it come to working out TOD? I am currently enjoying the Milviz 737 using no FMC, good old school flying.

 

But would like some guilds to calculating TOD.

 

 

Is there a general simple way to work out TOD?

 

Thanks.

Depends on your altitude and speed, I usually am at around 300IAS and FL 320 so I start down around 150NM out to give the passengers an nice easy (1500FPM) descent with no spoilers :-)

Yes ofc it down to speed and VS, I was hoping someone would have a simple formula.

Hey I don't fly the heavies. 

 

you have to use the GS (glideslope) and ooops damn i forgot everything. 

 

distance * speed / hour and i think the fpm blah blah oops seriously forget back to my notes.

 

Hey I think you will need the altitude to be multiplied by the GS 3 deg.  and you will get the miles. and divide your Ground speed by 2 and you will have your fpm.

 

 

 Oh crap back to the notes. sorry i am always a duh with maths .

Rule of thumb is 3nm forward per 1000' of altitude. You take your altitude you need to lose, multiply by 3. So if you're at 37000' and you have a restriction of 5000', in reality you only need to lose 32000' of altitude. Take 32000, drop the 0's giving you 32. Multiply 32x3=96. This is the approximate distance to cover the altitude lost, now I add a 5nm buffer, so I'd start at 101nm.

 

To calculate a descent profile, take your GS*6=ROD.  For example at 400kts GS*6= 2400fpm. Keep in mind as your GS decreases, the rate of descent will decrease as well.

 

It's good to redo these calculations every 10000' to ensure you're on the correct profile that you planned for.

 

Hope this helps.

I usually take the "three-by-one" rule for quick estimates: Use the difference between your current altitude and the airport elevation, divide it by 100 and multiply the result by 3. That is more or less the distance you will need for your descend. (Not exactly by that rule, but I tend to add another 10% or so to be on the safe side)

Thanks the last two reply that was what I was hoping for.