tadex

13th Jul 2007, 22:26

Hi Folks,

i know this topic has been discussed several times, but I'm still confused about some things... 737-300/500:

1. Common rule seems to be: ALT x3 = Distance needed for Altitude Loss. So far so good, but does this calculation include deceleration from descent speed to 250kts and to 180kts at GS capture? According to my operators books it does, but it doesn't really work out well if i do my crosscheck at say 8000ft and have 24NM to go. I always end up using speedbrake. Or does the Formula Alt x3 = Distance required (without considering speed reduction) only apply to TOP OF DESCENT calculation, considering that you make a pretty steep descent gradient initially and then have spare mileage to cover the speed reductions from descent speed to 250kts and from 250kts to 180kts?

2. What about a heavy aircraft? Do you add some miles? Any rules of thumb?

3. What is your mental maths during a high speed descent? The aircraft achieves a higher descent gradient, but on the other hand i also need more track miles to slow it down...so, do I overall need MORE or LESS mileage? Any rules of thumb?

I just started on the 737 and would really appreciate if someone could shed some light on this for me... :confused:

best regards

tadex

i know this topic has been discussed several times, but I'm still confused about some things... 737-300/500:

1. Common rule seems to be: ALT x3 = Distance needed for Altitude Loss. So far so good, but does this calculation include deceleration from descent speed to 250kts and to 180kts at GS capture? According to my operators books it does, but it doesn't really work out well if i do my crosscheck at say 8000ft and have 24NM to go. I always end up using speedbrake. Or does the Formula Alt x3 = Distance required (without considering speed reduction) only apply to TOP OF DESCENT calculation, considering that you make a pretty steep descent gradient initially and then have spare mileage to cover the speed reductions from descent speed to 250kts and from 250kts to 180kts?

2. What about a heavy aircraft? Do you add some miles? Any rules of thumb?

3. What is your mental maths during a high speed descent? The aircraft achieves a higher descent gradient, but on the other hand i also need more track miles to slow it down...so, do I overall need MORE or LESS mileage? Any rules of thumb?

I just started on the 737 and would really appreciate if someone could shed some light on this for me... :confused:

best regards

tadex