stretching from ATR42 to 72 is like a 70% increase in available seat and applying a 70% stretch onto Q400 would mean ot can seat 150? If it can carry as much passengers as a 73G with relatively lower fuel burn then it could have its attractiveness?
The ATR was stretched from 48 to 68 seats, so only an additional 20 seats, or 42%. 20 additional pax is also what you need to turn a standard Q400 into a 100 seater. You will need to stretch it by some 4 meters in the cabin, and make additional space for luggage too.
Do you have a source showing comparitive fuel burn on same sector length? the fuel burn statistics thread here on the forum doesn't show that sort of fuel burn for the Q400
From a Q400 QRH I got to look through last year, and the above mentioned Q400 Fuel Efficiency Manual. A quick search on pprune will give you roughly the same figures.
You can achieve much better numbers when cruising slowly, but then you sacrifice the speed vs the jets, and you still can't compare with an ATR for total fuel burn. Throw in a 4-5 meter stretch, 1680 kg of passengers and 300 kg of bags, and your fuel consumption is going to go up by quite a bit.
Just using some rough numbers, even when you throw in 20 more passengers and cruise at a slow speed, the Q400 stretch will barely be able to achieve the CASM of the ATR 72. 600kg/[email protected]
= 8,8 kg/hr/pax. The equivalent number for a Q400 at 800kg/[email protected]
pax is 10 kg/hr/pax. Even in the unlikely case that they can keep the burn at 800kg/hr for the 100 seater, you only reduce that to 8 kg/hr/pax. If the burn increases by just 80 kg, it will already exceed the CASM of a 68
seat ATR 72.