Hi Cetinski,
No, you're not missing anything. They do indeed use PH for the landing climb weight limit. You are right in thinking the DH would be a better value to use here. After all, those are the conditions we are in while attempting to reach that magical 3.2% climb gradient after a baulked landing.
One argument I read was that sufficient "fudge-factor" is already built into the charts to compensate for non-standard temperature. There is also the argument that the aircraft will be much lighter at arrival than at departure. However that says nothing about its ability to climb out at 3.2% in the landing configuration
These arguments are good but I don't think they get to the bottom of it.
If you look at CAO 20.7.4, an aircraft must be able to climb out at 6% after take-off in the take-off configuration with gear down, outside of ground effect and with take-off power set. There is no reference to ISA conditions. In other words the aircraft must be able to achieve at least this 6% in any conditions. Therefore, the manufacturer has to make sure the aircraft can achieve that 6% at all times under any temperature and pressure combination. Hence the climb weight limit line being affected by temperature and pressure.
If you now look at the landing climb performance, CAO 20.7.4 says the an aircraft must be able to climb at 3.2%
in ISA in the landing configuration, at take-off power and not exceeding 1.3 V
s. The manufacturer therefore only needs to ensure that 3.2% can be met in ISA conditions and so the landing climb weight limit graph is designed to represent ISA conditions only. That's why you don't have the temperature scale since in ISA for any pressure height, the standard temperature can be assumed.
Cheers,
Rich
