Now, regarding the 757-200 PCF, I have a question regarding the Main deck Cargo fire drill :
This is what the QRH initially directs the crew to do : (After donning oxygen masks and establishing crew communications.)
1. PACK control selector (either) ..... AUTO
2. PACK control selector (other) ..... OFF
3. L RECIRC FAN ............................ON
4. TRIM AIR Switch .......................... Off
5. MAIN CARGO FIRE AIRFLOW VALVES Switch .. ....Push.
It further says :
Note : The ventilating airflow to the main cargo compartment will shut off; the E/E overboard exhaust valve will open ; operation of the lower hold heater fans will be inhibited.
My question is ... why does the checklist ask for the LEFT RECIRC fan to be turned ON ? (and it is anyway ON by default during normal operations)
The note also says that the Overbrd exhaust valve will open after accomplishing the above steps. However, doesn't the overboard exhaust valve open only if the LEFT RECIRC fan is turned off ??