QRH normal landing distances

[Driver 170]

In the QRH Normal LDG distances on the top header adjustments you have (TEMP ADJ PER 10c, ABV ISA / BLW ISA)

Do i use airfield temperature or ISA DEV?

[MarkerInbound]

You make the adjustment for every 10 degrees (in the example you give) difference between the reported temperature and the ISA temperature for that airport.

[Driver 170]

So work out ISA DEV and find OAT at airfield and its the difference between the two that you use. I was assuming its ISA deviation alone from standard SL

Thanks.

[MarkerInbound]

In my my aircraft the numbers run about 250 feet for every 10 degrees above ISA/200 feet for every 10 below Autobrakes 2 on a dry runway. Why Boeing doesn't just say 25 or 20 feet per degree I don't know. EDI is sea level so if it is 25c add 250 for temperature adjustment. If the airport elevation is 2000 feet MSL and it is 30c you would add 475. 30- ((15-(2x2)) X 25.

[de facto]

You use ISA deviation.
If the airport is lets say at 2000 msl,and OAT is 21.C,(2x-2 +15c)=ISA of +11C.
Therefore the temp deviation from ISA is 21-11=10C.
Find the increase of landing distance based on 10C.

[Driver 170]

So you only use airfield OAT to find ISA dev. But you use ISA DEV for the actual landing distance adjustment. So in your example ISA +10

[B737900er]

Driver its not to difficult to work out.
Whatever the ISA DEV is for the airfield interpolate from the the table.
In the example given above, the ISA DEV is 10C so use 10C.

Lets say a sea level airfield is reading 25C the ISA DEV would be 10C correct?

[Driver 170]

Yeh got it just for some reason mentioned the answer again. Certainly makes sense using ISA DEV as most instruments are subject to error from standard SL