It was nothing to do with the airships.
The DA is used by the Met Office Research Station about a quarter mile from shed 2. They regularly fly tethered balloons with various instruments hung on the wire. They also do UAV testing.
The station there is a longstanding research base, an outstation of a Met Office department called Observation Based Research, run from their national HQ in Exeter.
And you can always ask Cranfield if the DA is hot or cold on 122.855; straightforward enough as they're the local basic service provider.
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