How does a higher temperature when programmed in the FMGC affect REC MAX FL? While I was reading the FCTM I came across this line mentioned below.


  An increase in the Outside Air Temperature (OAT), that results in a decrease of the REC MAX FL.


I wanted to know if we enter a higher than normal temperature for a particular FL or we even forget to put the minus sign in front of the temperature value (our older A320s with Honeywell FMS accepts the temperature without the minus sign) how does this cause the FMGC to compute a lower REC MAX FL?
FMS calculates REC MAX in cruise by calculating temperature from actual OAT and TROPO inserted in INIT A page. It assumes standard -2C/1000ft until inserted tropopause altitude which after it uses constant temperature. 

During climb it calculates temperature profile from inserted tropo/temp. If your REC MAX seems to be off during climb check the inserted values. Also, when A/C reaches CRZ ALT entered to PROG page it starts to use measured OAT at once, so REC MAX can change suddenly if it was off in INIT A page.

Note that REC MAX is only function of A/C weight, TROPO and OAT. Cost Index does not affect REC MAX.