McDonnell Douglas C-17 Globemaster III C-17A ER

C-17A ER is the name given to C-17A Globemaster III aircraft whose centre wing section was turned into a sealed fuel tank. It is not an official U.S. Air Force designation: according to the [Wikipedia entry on the C-17](https://en.wikipedia.org/wiki/Boeing_C-17_Globemaster_III), “ER” (extended range) is an informal Boeing name. In military documents these aircraft remain C-17As; what sets them apart is a series upgrade, applied first on the production line and later to aircraft already in service.

The first word of the change comes from a [Boeing press release of 23 March 2001](https://boeing.mediaroom.com/2001-03-23-U.S.-Air-Force-Accepts-Newest-Boeing-C-17-Globemaster-III), in which the manufacturer announced that the Air Force had accepted its newest C-17. Boeing explained that this aircraft and all future C-17s would be equipped with a new extended range fuel containment system in the centre wing area, and that they also carried the upgraded avionics required by the Global Air Traffic Management system. The wing modification therefore arrived together with an update of the equipment the aircraft needed to operate in civil airspace.

Nine months later, in the [release of 17 December 2001](https://boeing.mediaroom.com/2001-12-17-Boeing-Delivers-80th-C-17-Globemaster-III-to-U.S.-Air-Force) marking the delivery of the 80th C-17 to the Air Force, the company stated that all C-17s delivered in 2001 had the extended range fuel containment system “and other Block 12 upgrades”.

This is where a discrepancy needs to be recorded. Boeing, the primary source and the aircraft’s manufacturer, ties the centre wing tank to Block 12. The Wikipedia entry, however, states that the extended range configuration began in 2001 with Block 13, citing a work by Norton published in 2001 (page 93), a printed book we have not been able to consult. Until another primary source turns up, this page takes Boeing’s association with Block 12 as its reference and notes the version given by Wikipedia.

The capacity figure comes from the manufacturer itself, in its airplane rescue and fire fighting information sheet, “Airplane Rescue and Fire Fighting Information C-17/C-17 ER”, dated 2005, of which [a copy survives on archive.org](https://web.archive.org/web/20071025184815/http://www.boeing.com/commercial/airports/arff/arffc17.pdf). For the C-17 it gives fuel tanks of 13,492 US gallons, or 51,073 litres; for the C-17 ER, 18,319 gallons, or 68,770 litres, and its diagrams mark the extended range fuel tank. The document is written for airport emergency crews, who need to know where the aircraft carries its fuel and how much, and that is precisely why it distinguishes between the two configurations.

C-17s built before the change were brought up to the new standard as well. A [Robins Air Force Base article of 14 November 2014](https://web.archive.org/web/20240501072243/https://www.robins.af.mil/News/Article-Display/Article/840000/updating-globemasters-562nd-amxs-extends-c-17-range-adds-fire-protection/) described how the 562nd Aircraft Maintenance Squadron (562nd AMXS) was extending the range of the Globemasters and adding fire protection. One of the people interviewed summed it up by saying that, by adding 6,000 gallons of fuel, the aircraft would be able to fly extended range. It is a round figure, given in conversation, and it does not exactly match Boeing’s technical sheet; we therefore quote it only as a point of comparison, not as a capacity figure.

One gap remains open. Wikipedia credits the extended range models with a specific range, but the Boeing sheet it cites gives no range figure at all, and we have found no primary source to support it. This page therefore publishes no range for the C-17A ER: what is documented is the centre wing tank, its capacity according to the manufacturer, the moment it entered production and its later installation on aircraft already delivered.