B757 - 200 SF/PCF main deck fire suppression

[bluskiez]

Greetings everyone !

My first post on pprune.

I have two questions on the B757-200 freighter.

1. Why is the right recirculation fan removed from the 757-200 freighter ?

(Is it because of the very low volume of space between the main deck and the cargo pallets, which does not necessitate a recirculation fan ?)

2. The 757 -200 PCF (Precision conversion freighter ?) has a non normal checklist for MAIN DECK fire (Main Cargo Fire) and a separate one for the forward and aft cargo holds. (Cargo Fire)

Whereas, the 757-200 SF (the ones used by DHL, which were earlier passenger aircraft in British Airways fleet), have a common non normal checklist/drill for the Main Deck and the Fwd/Aft Cargo compartments.
In this case, the Left Recirc fan shuts off, one pack is turned off and other pack is commanded to Low Flow and cabin gradually depressurized to aircraft altitude.


Why is that so ?


Thanks

[Mr @ Spotty M]

It might well be that you do not need recirculated air within the main cargo deck.
The PCF versions does not have any seats in the main cargo deck, only in the flight deck.

[oceancrosser]

The 757F has no main cargo deck fire suppression. Only detection. You depressurize (hardly counts as a suppression) and hope that it is a false warning. Otherwise...

The right recirc fan was probably considered surplus to requirements.

[Daysleeper]

For Q2 could the PCF have retained the lower hold extinguishers?

[Mr @ Spotty M]

The PCF does still have a lower cargo fire suppression system.

[bluskiez]

Thanks for your replies.

@Daysleeper

For Q2 could the PCF have retained the lower hold extinguishers?

You're right. The -200 PCF have fire extinguishers for the lower holds.

[bluskiez]

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 ??

[HAWK21M]

BTW
B752PCF has a Fire Extinguishing system in the Bulk cargo holds unlike the B752SF.
Also the LH recirulation fan is located just aft of the FD panels & upstream of the OEV [Overboard exhaust valve].If the LH Recirulation fan is running it will provide the flow to clear the smoke through the OEV.

The RH Recirulation fan is NOT present on the B757 Freighter as its not serving the purpose.