Declared Conditions, calculating t/off & landing distances
In all the books I have about flying up to CPL, I cannot find a proper thorough guide to using the declared charts in CAO 20.7 (appendix)
We use the charts to find the declared conditions, add the elevation... All books state this, but....
Then what?
What do we do with that density height figure?
What do we do if our POH has Pressure height & temperature only in the performance section?
Bear with me because I have been doing it one way which I'll explain, but was recently introduced to another way by another "Bobby" who then told me another "Birdy" does it yet another way!!!
I was taught to to this way, which I'll call "my way" ( not that I invented this, it was taught to me, however, I will stand corrected )
1. Obtain the declared height (say 2500')
2. Add the Elevation (say 1500')
3. With this DH of 4000', I would use in the POH as pressure height intersecting with the corresponding ISA temperature at 4000' which is 7º
4. read off the table the take-off or landing distance.
This next way, I'll call "Bobby's way"
1 & 2 steps - same as above
3. The elevation is 1500' then the temp bobby would use is 12º - this temp came from a standard atmosphere SL temp of 15º corrected for the elevation, ie SL standard temp, less 3º for the 1500' elevation
4. Using 4000 PH on the POH table, read off the distances that intersect with 12º
Finally "Birdy's way"
1 & 2 steps - same as above
3. The elevation is 1500' birdy uses 15º - the standard SL temp
4. Using 4000 PH on the POH table, Birdy reads off the distances that intersect with 15º
"My way" is what I've been using forever (DH4000' convert to PH4000' using ISA 7º at that DH)
"Bobby's way" is slightly safer as the temp is higher (PH4000' 12º)
"Birdy's way" - safer again using a higher temp (PH4000' 15º)
Which way do you use?
Where is a good resource to refer, ATC, Bob Tait dont fully discuss this...