A reality check:
The dry operating weight of FZ's B738's is in the region of 42.2 Tonnes.
Whilst it can ostensibly hold a maximum of 21 tons of fuel, the reality is that the high temperatures in DXB (
and / or the Far East) lead to the fuel having a low SG and, as such, the most likely figure for full tanks is 20 tons.
The aircraft are presently configured with 189 passenger seats, in an all economy configuration (
which, if one take a 50:50 split of male:female notional weights, means that a full load of pax would ostensibly weigh in at 14.9 tons).
The maximum take-off weight of the aircraft is 79 tons.
So let's do some rough math on those numbers:
----- The wings full of fuel scenario -----
DOW (42.2T) + Fuel (20.0T) = APS (62.2T)
Possible payload = 79T - 62.2T = 16.8 Tons (
always assuming that the take-off is not performance limited and that one can actually take-off at the aircraft's max-structural weight… which is not always possible ex-DXB on a hot day and / or with a QNH below standard).
So, with a full load of fuel, and typically 4.5 tons of bags & cargo, that takes the maximum allowable weight for passengers down to 12.3 tons…
This would mean that there will have to be a lot of (33) empty seats, i.e. 17.5% of the aircraft's seats will have to remain empty, in order to allow the flight to get airborne with the maximum possible fuel load (
and always assume that the flight is not take-off performance limited, which would only make matters worse in terms of passenger load factor!).
In terms of range (
with full tanks, and as many passengers as allowed by the take-off performance), given that the rules say that the aircraft can't land with dry tanks, let's (
generously) assume that the fuel need for Alternate + Final Reserve is (
only) 2.4 tons… which means that the fuel available for the sector is 17.6 tons.
When operating at high gross weights, the aircraft will burn (
approx) 2.5 tons per hour, and so the available fuel for the sector equates to a maximum of 7 hours of flight time for the sector.
So it's got the legs, but not with full a full passenger load.
----- The 189 bums on seats scenario -----
If all 189 seats have bums on them, plus 4.5 tons of bags & cargo, then the ZFW is typically going to be in the order of 61.6 tons.
That then leaves 17.4 tons available for fuel (
i.e. before the max structural take-off weight is reached, and which again assumes that the aircraft is not take-off performance limited).
Given that the rules say that the aircraft can't land with dry tanks, let's (
generously) assume that the fuel need for Alternate + Final Reserve is (
only) 2.4 tons… which means that the fuel available for the sector is 15 tons.
Again, when operating at high gross weights, the aircraft will burn (
approx) 2.5 tons per hour, and so the available fuel for the sector equates to a maximum of 6 hours of flight time (
but not including taxi times).
Thus, fill all the seats and the range is limiting.
Maybe if the aircraft was re-configured with a lot less seats (
overall), e.g. perhaps as per the much touted change to having a 'Business Class', then that might provide a sufficient enough change in the aircraft's Dry Operating Weight... but it'd require a big change and the loss (
or change) of a lot of seats, imho ?!
----- And what of the crew's FDP limits ? -----
The maximum allowable Flight Duty Period for 2 sectors, with 2 flight crew, starting at the most optimal time of start, is: 13:15 hours.
1 hour of that FDP is consumed in the pre-flight briefing, and another 45 minutes is consumed during the turn-around. That then leaves you with 11:30 to play with, i.e. for operating each sector (
including taxi-out / flight / taxi-in), i.e. ostensibly 5:45 in each direction (
and that's with a tight turn-around), before the flight crew hit the buffers on their FDP limit.
With an 'augmented' Flight Crew (
i.e. carrying an extra Flight Crew member, which almost certainly would have to be a Captain, unless they start LHS checking the F/O's ?!) it is possible to extend the FDP by the use of in-flight rest.
That said, the following restrictions apply:
When any additional crew member is carried to provide in-flight relief, with the intent of extending an FDP, that individual shall hold qualifications which are equal or superior to those held by the crew member who is to be rested. The division of duty and rest between those crew members being relieved will be kept in balance. It is unnecessary for the relieving crew member to rest in between the times relief is provided for other crew members.
When in-flight relief is utilised the crew member resting must be provided with comfortable reclining seat, or bunk, separated and screened from the flight deck and passengers and free from disturbance.
A total in-flight rest of less than 3 hours does not allow for the extension of an FDP, but where the total in-flight rest, which need not be consecutive, is 3
hours or more, then the FDP may be extended as follows:
Rest in a Seat: A period equal to one third of the total of rest taken, provided that the maximum FDP permissible shall be 15 hours (16 hours for cabin crew).
Needless to say, FZ's B737's do not provide such facilities as a comfortable reclining seat, in a screened off area, free from disturbance.
The other method would be to have a whole extra set of Flight Crew position outbound (
to then operate the return flight), and therein as they'd only operate the one (
return) sector, that means that their maximum allowable FDP would increase (
by 45 minutes) to become 14 hours; but wherein the time of reporting for positioning (
i.e. one hour prior to STD of the outbound sector) is the point when the clock starts to tick for the purposes of that 14 hour FDP maximum.
Nb. A quick look at the
Great Circle Track from DXB to BKK - based on a (
still air) Ground Speed of 430 Kts (
which is typical of a B738) - shows a distance of 2651 Nm and a 'flight time' of 6:10.
Thus (
based upon 'still air') an out and back from DXB to BKK would take:
1:00 hour pre-flight briefing
0:10 minute taxi-out
6:10 flight time
0:05 taxi-in
0:45 turnaround
0:10 minute taxi-out
6:10 flight time
0:05 taxi-in
= 14:35
And that's assuming absolutely everything went like clockwork ?!
Needless to say, I can't see many Commanders being overly keen to exercise 'discretion' in any of the above crewing scenarios, to say nothing of the limitations of carrying just a single set of cabin crew (
and their FDP limits therein)... especially with the delights of the PatPong Road being so close ?!
Ps.
High Energy: I concur with your assessment, wrt the B757... an awesome aircraft and one that I loved flying... but, failing that, some A330's would be equally welcome !