Modern Aircraft Designations-exceptions to the rule
With almost any system, exceptions and errors tend to crop up. And the Mission, Design and Series (MDS) system is no exception.
The first notable exception to the rules occurs in the Design Number – for a couple of the Basic Mission Designations, the number “1” was immediately skipped – there is no P-1 or S-1.
And there are some gaps in the sequence that are understandable – cases where it was assigned, but the aircraft was later cancelled.
The E-7 designation is one such example.
Another notable exception is that there seems to be an unwritten rule that the "-13" designators are always skipped.
And while we’re on the topic of design number exceptions, there’s the F-35 Lightning II - which was originally the X-35, an experimental aircraft developed by Lockheed Martin for the Joint Strike Fighter Program. When it became fighter-capable, the “X” was converted to “F” (had it followed the sequence, it would have been the F-24).
The AV-8 Harrier is another exception that seems based more on confusion – originally, it was designated as AV-6B, likely because it was a direct development of the Hawker-Siddeley Kestrel, which had been tested in the U.S. under the designation XV-6A. However, it was later decided to designate the Harrier in the attack series – and at that time, the next available number was A-8. Problem was, the Harrier was still a VTOL aircraft, which are represented in the designation system by the "V" vehicle type symbol.
So rather than becoming an A-8, it became the AV-8... instead of AV-6.
For an example of a Basic Mission Designation exception, there’s the F/A-18 Hornet. According to one story, the origin of the Hornet's F/A-18 designation was due to there originally being two different versions of the aircraft planned – the F-18 and A-18.
However, the capabilities of the two were eventually combined in a single production version to be known as the F/A-18 (as an aside, the A-18 designation would have been out-of-sequence anyway).
However, in another version of the story, the “real reason” for the “F/A” designation was that when it had become clear that the air-to-air (Fighter) and air-to-ground (Attack) roles of the Hornet would be integrated into a single variant, the Navy pilots in the "Attack community" refused to a fly an F- designated aircraft, and the Navy pilots in the “Fighter community” refused to fly an A- designated aircraft. And while it could have been designated “AF” (which seems redundant, because as I understand it, The "F" designator explicitly includes fighters with ground-attack capability), it seems that wasn’t acceptable either, because to the "Attack community", it still looked like no more than an adapted fighter (which, to me, it seems it actually is), while those in the "Fighter community" complained that the "A" came first! As it turned out, the only "acceptable" designation prefix was "F/A".
So where is the true story? Somewhere in the middle, I feel.
It was pointed out to me (forcefully, rather than tactfully) that I left a Basic Mission designator out of the previous article – that of “K”.
Well – yes, originally, the system did allow for a “K” for Tanker as a basic mission. However, all U.S. military tankers have been derivatives of other aircraft - KA-3, KB-29, KC-130 as examples. So, since there was never a designation allocated, the K-series Basic Mission designator was cancelled sometime between 1977 and 1986 due to non-use.
How about a double exception? The F-117 Nighthawk – even though it was called a Stealth Fighter - had no air-to-air role whatsoever, and should have received an "A" for its Basic Mission Designation. And the Design Number of 117 was outside the sequence of both the Attack and Fighter series. As an Attack craft, it should have been designated as an A-11.
And then there’s the SR-71 Blackbird – it was originally to have been a continuation of the pre-1962 bomber series (that ended with the XB-70 Valkyrie), but was proposed for the reconnaissance/strike role, with an RS-71 designation.
As the story goes, though, President Lyndon B. Johnson messed up the designation in his public announcement and called it the SR-71 - and because nobody wanted to correct the president, the reconnaissance plane (RS-) that flew at the edge of outer space became the spaceplane that performed reconnaissance (SR-).
And since I’ve mentioned redesignation to a non-existent designation, I’m going back to the fighters – the F-111 Aardvark had a strategic bomber variation. However, there was no option for a “Bomber” in the Modified Mission Designation (though there wasn’t a reason not to simply create one that I can see), so instead of being a BF-111, it was designated as a FB-111.
The Series Indicator also has had some exceptions in order to designate a specific customer, for example the F-15N Sea Eagle – the “N” was used out of sequence to indicate it as specific to the US Navy.
And, though it’s not a US Military aircraft, the Israeli Air Force has the F-15I, using a “normally” excluded character “I”.
There are more designations, which do not strictly follow the official rules and regulations – I leave it to the reader to have fun searching for their own amusement.