However as Ozair already pointed out countries that have a heavy tanking need tend to be purchasing KC330s right now, and I suspect countries that have a heavy tanking need but can't afford new frames will purchase ex-airliner 767s for conversion (as the Israelis have done). I'm convinced India will be a KC330 purchaser, although I can see a purchase of used A330 or 767 frames being a somewhat dark horse candidate. I can also see Pakistan purchasing used A330 or 767 frames for conversion.
Just to clarify, there is no current used 767 conversion, at least for a boom equipped aircraft. Boeing blocked IAI from doing so back in 2018, with Israel subsequently ordering KC-46s. I haven’t seen an approved conversion offer from any other vendor.
The conversion of both the 767 and the A330 to tankers is not cheap and I believe why we see so many new tankers being acquired and so few conversions. For the 767 IAI suggested a cost of US$150 million which likely included a used 767.
https://www.jewishpress.com/news/us-new ... 018/08/06/
IAI’s proposal was based on purchasing used Boeing 767 aircraft on the open market, and converting the planes for use as refueling tankers, at a discounted cost of $150 million.
Australia acquired and converted two ex-Qantas A330s for $200 million each (about the US$150 million each as well given the dollar conversions)
http://www.aviationwa.org.au/2015/07/01 ... -for-raaf/
The RAAF is purchasing two ex-Qantas Airbus A330-200 aircraft, VH-EBH (MSN 892) and VH-EBI (MSN 898), from lessor CIT Aerospace by the end of 2015, for conversion to KC-30A multi-role tanker transports (MRTT) at a total cost of $408 million. Airbus says an MRTT conversion takes 10-12 months.
The KC-10 airframe brings with it the disadvantages of a third, hard-to-access engine with not alot of added benefit compared to the A330 or 767. If an air force is going to be so cash strapped to have used KC-10s look attractive over brand-new KC330s or KC-46s, they'll probably be less inclined to deal with the KC-10 maintenance and operational headaches over used A330 or 767 conversions. Hell, the USAF, the most well-funded air force in history, is one of those nations which is literally what started this topic to begin with.
So based on the previous cost of conversion I don’t think cash strapped Air Forces consider a used A330 or 767 as value for money. Yes cheaper than a new build but likely difficult to acquire and hence why no one other than the RAAF, who supplemented their existing new build fleet, are acquiring any. Perhaps COVID-19 will reduce the acquisition cost of some of these A330s and make a conversion more economical but that seems unlikely to me. The big cost is probably the conversion and that is where Boeing and Airbus have the Air Forces under their thumb.
A used KC-10 is a big aircraft for a small Air Force and probably a reasonably difficult aircraft to sustain, as you suggest. It really is positioned well to be retired from the USAF and move to a CONUS commercial company, especially as DC-10s also leave the FEDEX fleet.
What we also haven’t seen is a push to acquire more KC-130 and A400M aircraft for the tanking role. Half of that is probably cost in the case of the A400M and the other half likely the lack of a boom. A lot of small Air Forces operate F-16s and the lack of a probe for refuelling means a bigger and more costly acquisition.
I believe the Dutch also had KC-10s (from converted ex-airliner DC-10s) but ended up divesting them as well.
You know where those ex-Dutch airframes ended up, by the way? Omega Air Tanker. In fact it's effectively the core of their initial and current fleet.
The Dutch have had a good run with the KDC-10, serving 25 years before the first was passed to Omega with the second going next year. Omega did run ex RAAF 707s and a KC-10 with drogue refuelling before they acquired the KDC-10s. Hence only now do they operate a boom equipped aircraft.
As counter-intuitive as it may seem as a private entity Omega Air Tanker doesn't have the funding issues of governments, even the largest ones. Or rather, they're better able to incorporate those costs into their overheads because they don't have the competing mandates of spending as little of that massive budget as possible nor other acquisition programs competing over that budget. Being able to offer a fixed-price package (even with modifiers, qualifiers, caveats, stipulations, conditions etc.) brings economic operating benefits.
Additionally operating the KDC-10s for a few years before they potentially acquire any ex-USAF KC-10s will be a massive help. They will have a very good idea of the operating costs and likely be better positioned, and provide the most comprehensive, realistic and low risk quote to the USAF for commercial AAR services.