Why does a jet need more fuel to land while still carrying bombs?
July 21, 2013 12:39 PM   Subscribe

The latest ragebait going around is this story that a US training sortie burned too much fuel waiting for the range to be cleared, so they couldn't land safely without dropping their bombs into the sea near the Great Barrier Reef. My question is, how does dropping the bombs help the planes land?

It would make sense if they didn't have enough fuel to carry home the extra weight, but the newspapers I've found phrased it as if the landing itself needed more fuel. For example, NBC wrote, "the Harriers could not land with the ordnance and they could not continue to wait with their shortage of fuel." CNN wrote, "they were running out of fuel and could not land with the amount of ordnance on board." There is, notably, no mention of diverting to a closer site.

(Also, it sounds like all the newspapers are quoting the same one press release; does anyone have a link to the original press release?)
posted by d. z. wang to Technology (12 answers total) 1 user marked this as a favorite
Aircraft have a maximum landing weight(MLW). Dropping the bombs may have been necessary to get down to the MLW. The aircraft carrier would have been the only landing site within range of the planes.
posted by monotreme at 12:46 PM on July 21, 2013

My read is not that they needed more fuel to land with bombs than without, but that they didn't have the fuel to drop the bombs at their intended destination and still make it back to the landing strip. Presumably landing the particular plane they were flying was considered too dangerous with the bombs still aboard.
posted by logicpunk at 12:50 PM on July 21, 2013

I think you're misreading that quote. They couldn't keep waiting because they were short on fuel. They also couldn't land with the ordinance still on the aircraft. They probably needed to drop the weight to land no matter how much fuel they had left. They'd need to maintain a higher speed to maintain lift with that extra weight but at that speed they wouldn't have enough space on the runway to stop. Or, if they were landing on an aircraft carrier, the weight of the aircraft and the bombs would have been too much for the arresting wires.

And, since we're talking about the Harrier Jump Jet (which has VTOL capabilities) it can land vertically but it takes a LOT of fuel.
posted by VTX at 12:53 PM on July 21, 2013 [3 favorites]

There may be safety considerations around landing with bombs, particularly if something goes wrong with the landing.
posted by corb at 12:57 PM on July 21, 2013 [1 favorite]

Best answer: FTA, they were using AV-8B's, which don't use arresting wires. In fact the sort of carrier that they were going back too doesn't even have arresting wires.

I used to work on a flight deck, landing with live ordnance is perfectly normal.

VTX is close to the right answer. More weight means for power needed from the engines, more power means more fuel consumed and this reduces your range.

Pilots calculate the amount of fuel required to return to base (Bingo), once they reach this number they have to return to base. This number assumes that they are flying as efficiently as possible. So they jettisoned the bombs to reduce weight and drag, which increases their range and got them home safely.
posted by Confess, Fletch at 1:07 PM on July 21, 2013 [4 favorites]

I think VTX has it, they needed to jettison the weight. Weight carried = extra fuel burn, and in the case of external ordnance extra drag as well (which requires even more extra fuel).

Carrier based Harriers land vertically, and cannot land with arresting wires (AFAIK) -- which makes their MLW extra-critical -- supporting yourself on a pillar of downward blasted air is hard enough without extra weight. (For a tangential but illuminating example, a Harrier can take off normally with a bit over 10,000 lbs more than if it were taking off vertically.)
posted by wrok at 1:14 PM on July 21, 2013

There might be "no mention of diverting to a closer site" because there wasn't any such closer site --- since the aircraft was coming in with an emergency (the low fuel), then landing where emergency personnel and equipment (firefighting, medical, etc.) would be available makes a heck of a lot of sense. Or, considering where they were, there might not have been any suitable landing strips within reach.
posted by easily confused at 2:54 PM on July 21, 2013

Best answer: They were flying off of USS Bonhomme Richard, which isn't an aircraft carrier even though it looks a bit like one.

It isn't possible to operate normal jets off of an LHD. LHD stands for "Landing Helicopter Dock" which refers to the fact that it has a docking area for 3 LCAC's (Landing Craft Air Cushion). In terms of aircraft, as the name suggests usually it's primarily or exclusively helicopters.

The flight deck is too short for normal aircraft to land, and the ship doesn't have catapaults to get them into the air.

The only reason they can operate Harriers is because those land vertically, and because they use partial hover-mode when taking off. But as others above have pointed out, a Harrier can only land vertically if it is below a critical weight. So they had to dump their ordnance in order to get below that critical weight.

I don't understand why anyone would rage about this. The bombs didn't detonate, and they're not going to detonate, and they were dumped in deep water, away from everything. So who cares?
posted by Chocolate Pickle at 4:11 PM on July 21, 2013 [2 favorites]

So who cares?

Well, it's not just some coral, it's the Great Barrier Reef, one of the largest coral ecosystems in the world. It's an Australian Marine Park, as well as a UNESCO World Heritage Site. And despite those protections and recognition that it's one of the best managed reef systems worldwide (largely thanks to being in a rich country rather than an impoverished Pacific island country, for example), it's under constant threat from sea traffic, human tourism, remaining allowed fishing, and above all, climate change.

I think that you're essentially correct that this represents a manageable situation, but it betokens an apparent lack of respect for the culture of environmental protection that the Marine Park has been trying to instill for the last few decades. This gets amped up by those who are generally opposed to the US, to US imperialism, or to militarism on general principle.

I imagine, d.z. wang, that more specifics about the incident will come out as it's studied; it may depend on what sort of investigation the Australian government demands, although it's almost certain to be carried out by the U.S. Navy itself.
posted by dhartung at 5:12 PM on July 21, 2013 [5 favorites]

Response by poster: Chocolate Pickle: "I don't understand why anyone would rage about this"

Yeah, I use "ragebait" in the same pejorative sense that I would use "linkbait," to mean that I don't really think it's rage-worthy.

Thanks for the explanations, guys.
posted by d. z. wang at 7:51 PM on July 21, 2013

AV-8B's are known as Widow-makers so taking every possible precaution was a good idea.

See also: Nightmare's Prayer: A Marine Harrier Pilot's War in Afghanistan.
posted by mlis at 10:35 PM on July 21, 2013 [2 favorites]

Mod note: Comment deleted; let's just stick to answering the question.
posted by taz (staff) at 4:54 AM on July 22, 2013

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