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The C-17 had to overcome flight-control problems, wings that were unable to carry their designed maximum load, automation growing pains, and a crew size reduced to just two pilots and a loadmaster so I don't understand why the USAF still uses C-17s and not just KC-10s or invest in the A-400M Atlas instead.

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    $\begingroup$ You seem to be ignoring the fact that the C-17 was fully operational a good 20 years before the A400M. The A400M doesn’t seem to have been an option when the USAF was acquiring the C-17, and why would they throw away all that investment after it was acquired and all the bugs had been worked out? The A400M had plenty of problems of its own. $\endgroup$
    – nobody
    Commented Apr 23 at 20:55
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    $\begingroup$ Problems were fixed long ago and a C17 is twice as big as an A400m. KC10 are out of production. $\endgroup$
    – Pilothead
    Commented Apr 24 at 15:41
  • $\begingroup$ The C-17 still has major software problems $\endgroup$
    – VFA-34
    Commented Apr 24 at 15:49
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    $\begingroup$ why the USAF still uses C-17s and not just KC-10s There is very little overlap in what those aircraft can do. You can't land a DC-10 on unpaved runways. Nor does it have roll on-roll off for cargo. $\endgroup$
    – zymhan
    Commented Apr 24 at 19:45

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The C-17 is made by a US company, Boeing. The A-400 is not.

KC-10 is long out of production.

Every aircraft in the history of ever had growing pains. If we bailed at the first "problem", there would be nothing in the air.

For "growing pains", the A-400M:

The aircraft has experienced technical problems, schedule delays, and cost overruns since the programme was launched in 2003.

From https://www.janes.com/defence-news/news-detail/airbus-takes-another-a400m-charge

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This answer covers some significant differences in the aircraft. The key difference there is maximum cargo weight.

The A-400M has a maximum cargo of 81,600 lb. The C-17 has a maximum cargo of 175,000 lb. Thus, the C-17 can carry more than double the weight (like an M1 Abrams tank). Remember, the US military is often projecting power half a world away. You need to be able to move that heavy hardware at a moment's notice. The downside is that makes for a shorter range and longer runway requirements, as well as more fuel consumption.

This is also why the USAF still operates the even larger C-5 Galaxy (maximum cargo of 281,001 lbs).

The A-400M is designed more for range, versatility and economy (turboprops are more efficient). It can move troops and light armor (humvees, etc). In other words, they serve different roles.

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Just to add something to the other answers.

The C-17 has been born as an answer to a Request For Proposal (RFP) from the USAF. "By 1980, the USAF had a large fleet of aging C-141 Starlifter cargo aircraft. Compounding matters, increased strategic airlift capabilities was needed to fulfill its rapid-deployment airlift requirements. The USAF set mission requirements and released a request for proposals (RFP) for C-X in October 1980"

why the USAF... not just invest in the A-400M Atlas instead?

Regarding the A400M: in the US, when a new military aircraft (or military aerospatial equipment) is requested, only the relevant national aerospace companies (if any) are normally (but not exclusively) allowed to submit a proposal. This was true for the C-X program and that obviously excluded any non-US design from the competition: no matter how good the A400M might have been, it was not an US design. Plus, the first idea for what would have become the A400M dates to the 1982, i.e. much later than the original RFP from the USAF.

why the USAF still uses C-17s and not just KC-10s?

Regarding the KC-10: "Alternative proposals were pursued to fill airlift needs after the C-X contest. These were lengthening of C-141As into C-141Bs, ordering more C-5s, continued purchases of KC-10s, and expansion of the Civil Reserve Air Fleet". So the idea to buy more KC-10 was actually there. Why it wasn't pursued further is not specified but I suppose it was a mix of political and technical aspects. I can't say anything about the possible political reasons but from a technical point of view the lack of a rear ramp and a conventional tailplane is for sure a big no-go for a cargo airplane.


Quoted text from Wikipedia

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    $\begingroup$ "only the relevant national aerospace companies are allowed to submit a proposal" Eight non-US governments bought the C-17, and four of those have access to domestic heavy aircraft manufacturing. $\endgroup$ Commented Apr 24 at 1:54
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    $\begingroup$ @AnonymousPhysicist: and what does this have to do with the design phase? The final product can be sold to whichever ally you want but it must be made in US (or whatever country issue the RFP). Please note that also the "winning answer" mentions this aspects. $\endgroup$
    – sophit
    Commented Apr 24 at 5:08
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    $\begingroup$ @MikeB: obviously if a country has no aerospace industry it cannot issue an RFP for its non-existing aerospace industry... do we really have to play these semantic games? $\endgroup$
    – sophit
    Commented Apr 24 at 9:59
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    $\begingroup$ @sophit Brazil has a relevant aerospace industry, but in their RFPs regulary participate other country industries (France, US, even Russia ...) $\endgroup$
    – EarlGrey
    Commented Apr 24 at 10:06
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    $\begingroup$ @sophit "Regarding the A400M: As usual in the military world, when a new aircraft or equipment is requested, only the relevant national aerospace companies (if any) are normally allowed to submit a proposal. " The "military world" does not end with the "US military world" (although the military industrial complex influence is projected well beyond the US en.wikipedia.org/wiki/Military%E2%80%93industrial_complex ) $\endgroup$
    – EarlGrey
    Commented Apr 24 at 10:24
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The USAF already has a fleet of C-17 aircraft. In FY21 they reported a mission capability rate of 80%. This is higher than the C-130H/J and C-5M which are the other main transport aircraft it operates (and even slightly better than the KC-10). Compare this to the A400M which is at... 35%? 70%? So the USAF already has a fleet and it performs the missions they need it to do. What incentive do they have to replace it?

Although it has a similar cargo weight capacity, the KC-10 is a very different aircraft. The fleet is only a quarter the size of the C-17 and it's way too late to produce more of them. It also lacks a very important feature that the other military airlift aircraft has, which is a built-in ramp to allow cargo to be loaded directly into the aircraft. The KC-10 requires large support equipment to load and unload cargo. The KC-10 is also not designed for operating from short or unpaved fields.

The A400M has the important design features for a military airlift (ramp loading, short/unimproved field capability), but it has less than half the cargo capacity. And this isn't just a matter of needing to buy more of them, since heavy vehicles like tanks are beyond the capacity of the A400M. The smaller size means it also has less range than the C-17. And lastly a more minor point is that the USAF uses boom refueling and would likely require this capability, so they wouldn't be ordering the A400M just off-the-shelf with the probe system currently in production.

Another argument for how these aircraft fill different roles is that the UK RAF currently operates both the C-17 and A400M, finding a use case for both aircraft. The French even borrowed a couple of their C-17s when they needed to move some heavy vehicles.

The only real alternative to the C-17 is a completely new aircraft, which will certainly come along eventually as the C-17 fleet ages. But this is extremely expensive and has all the risks that come with a new program.

And as has been pointed out, no aircraft program of this scale is ever without its issues, including the A400M. The only hull loss of a C-17 in almost 30 years of service was due to pilot error. The A400M has been in service just over 10 years and already had a fatal crash due to a software/maintenance issue. That's not say that the A400M has more issues: both are well in the realm of "small numbers" so it's hard to conclude much from this other than to say that they have both been fairly successful in their respective missions.

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  • KC-10 went out of production before the C-17 entered production. It's also a completely different class of aircraft and can't carry the large size loads the C-17 can and land them on unimproved short runways
  • A400M is much smaller, has shorter range, and didn't exist when the C-17 fleet was built. It's not a C-17 competitor, it's a C-130 competitor (and countries that buy it tend to buy it to replace their older C-130 models)

IOW, you're comparing apples and oranges. May as well ask why the army uses Hummers when they could buy Mustangs instead.

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  • $\begingroup$ I like the analogy and thank you for this helpful answer $\endgroup$
    – VFA-34
    Commented Apr 26 at 13:38

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