Free Cockpit Confidential by Patrick Smith

has the final say and can request more still. Carrying surplus fuel costs money, but not nearly as much as the hassles of diverting.
    The preflight paperwork includes a detailed breakdown of anticipated burn, which is carefully tracked once the flight is underway. Remaining fuel is compared to predetermined target values as the flight progresses from waypoint to waypoint. The totals are monitored by the crew and dispatchers, the latter receiving updates via datalink transmission. You have a solid idea, well in advance, of exactly how much fuel you’ll be landing with. If for some reason that number drops below or close to what’s legally required (unexpected headwinds, a mechanical issue), there’s ample time to plan a diversion.
    Do airlines cheat to save money? You’ll periodically come across scandalous-sounding news stories describing planes dispatched with “reduced fuel loads,” allegedly resulting in unsafe situations when these flights are hit with delays and holding patterns. Carriers are, in some situations, cutting back on the carriage of extra fuel, which is heavy and expensive to haul around. But note the word extra . It’s the above-and-beyond fuel that airlines look to reduce, not regulatory fuel. While these cutbacks allow for less wiggle room, they are not dangerous. The penalty isn’t crashing; it’s having to divert earlier than you’d like, with logistical hassles for passengers and crew.
    Given all of that, the idea of running the tanks dry would seem far-fetched. Yet a small number of fuel depletion accidents have occurred. Understanding how and why they occurred would entail pages of boring (for both of us) analysis that I haven’t the space to explore. These were once-in-a-billion mishaps. Most of them happened decades ago, and suffice it to say the stories were a lot more complicated than an airline being cheap or a copilot waking from a nap and exclaiming, “Holy shit, we’re almost out of gas.”
I understand that planes can jettison fuel. Is this done to lighten the load for landing? Sometimes you can see it pouring from the wingtips just before touchdown.
    People will sometimes complain to authorities about what they take to be streams of jet fuel trailing behind airplanes low to the ground. What they’re actually looking at are trails of water vapor—the condensed cores of the vortices spinning from the wingtips ( see wakes and vortices ). This is common when humidity is high. You will sooner see sacks of hundred-dollar bills being heaved overboard than fuel being spit away for no good reason.
    And then, yes, it’s to lighten the load. The maximum weight for takeoff is often greater than the one for landing—for a few reasons, the obvious one being that touching down puts higher stresses on an airframe than taking off. Normally, a suitable amount of fuel is burned away en route. Now, let’s say something happens after takeoff and a plane must return to the airport. If the trouble is urgent enough, the crew will go ahead and land heavy. But almost always there’s time to get within landing limits, and rather than tossing passengers or cargo overboard, the easiest way of doing this is to jettison fuel through plumbing in the wings. (I once had to dispose of more than 100,000 pounds this way over Northern Maine after an engine malfunction, a procedure that took many minutes and afforded me a lavish night’s stay at the Bangor Airport Hilton.) Dumping takes place at a high enough altitude to allow the kerosene to mist and dissipate long before it reaches the ground, and no, engine exhaust will not set the discharge aflame.
    Not all airliners have this capability—just the bigger ones. The 747, the 777, the A340, and the A330 all can dump fuel. A 737, an A320, or an RJ cannot. These smaller jets must circle or, if need be, land overweight. For some, landing and takeoff limits are the same, in which case it