Originally Posted by
simon001
Okay. Let me ask a "practice vs. theory" question on fuel:
If the forecast weather was ideal, both along the route of flight and at the destination, and the traffic at the destination expected to be light, might an airline pilot really only carry just 45 minutes of reserve fuel?
Legally you can. In reality that's not what happens. The company's I worked at had a minimum of one hour of fuel consumption at normal cruise altitude. Fuel flow at normal cruise altitude is close to the fuel burn you'd have while holding. But if you're going to be slowed down requiring flaps to be extended fuel flow will increase (eg, one aircraft mentions fuel flow increasing by 7% with flaps 1).
Diversion fuel is also predicted on a perfect plan via the filed route. No delays, no off track diversions, etc. That often doesn't happen in reality so guys add a bit of additional gas to their expected fuel burn to divert. My last diversion we were kept in the hold for another turn and then vectored for about 20 miles in the exact opposite direction that we wanted to fly. That burned up approx. 1,000 lbs of fuel that is not included in the planned release fuel. This is why Captains frequently divert slightly prior to the absolute minimum allowed.
What happens if the divert field is now backing up with inbound traffic? We were the 7th flight to divert into the airport on my last divert. It turns out that there was no other traffic but unforeseen delays and vectors could have added to more unexpected fuel burn. Which is why it's not uncommon, if the situation means that you'll probably diverting regardless how long you hold, to hear 'if you're going go early.' The first to land is often the first refueled and the first relaunched. We were the 6th of 7 to divert and the last to leave.