What is flight inspection, as provided by Cobham Aviation Services?
From their website, 


  Cobham conducts commissioning, return-to-service, engineering and
  periodic flight inspections in addition to trials work on a range of
  systems including, CAT I/II/III ILS, MLS, PAR, DVOR, NDB, U/VDF,
  TACAN, DME, AGL and PAPI and PSR/SSR.
  
  The specialist capabilities include procedure validation, ADS-B and
  MLAT-systems, ship borne navaids, FI programme management, technical
  investigations, communication tests and trials, windfarm trials,
  flight inspection advice, and training.
  
  Cobham has formal approvals from UK CAA Safety Regulation Group (CAP
  670), UK MoD, INAC (Portugal), ENAV (Italy), British Standards
  Institute (BS EN ISO 9001:2008), Germany BAF, and Air Safety Support
  International OTAR for UK Overseas Territories.


It looks like they test airport/en-route equipment such as approach systems and ADS-B systems etc. This can presumably be done in any aircraft equipped to fly/test those approaches and systems.