All classes, for general ref, inc A3B
A1B: fit for full flying duties (A1) and ground duties (B). (The medical pre-requisite for entry to the General Duties Branch and for qualifying as aircrew.)
A2B: fit for limited flying duties, fit for ground duties
A3B: fit for flying as combatant passenger, fit for ground duties (The class for Observers and Air Gunners)
A4B: fit for flying as non-combatant passenger, fit for ground duties
AhBh: fit for Home service only
AtB: temporarily unfit for flying duty (ie fit only for non-flying duties)
AtBt: temporarily unfit for flying and ground duty (implies sick leave at least and possibly hospital)
ApBp: permanently unfit
The classes were laid down in
The King’s Regulations and Air Council Instructions (Air Publication 958) KR& ACI par 1434 (1943 edn, above)
Other RAF usages etc for ref:
By 1944 para 1434 read as follows
"1434. Findings of Boards.
Officers will be classified in respect of their medical fitness to perform both air and ground duties within the standards laid down, in accordance with the following procedure :—
(a) The letter “A” will represent “Fitness For Air Duties” and “B” will represent “Fitness For Ground duties.
(b) A series of numerals qualifying fitness for air duties will be added, as requisite, after the letter “A,” viz,
1... full flying duties.
2... limited flying duties.
3....combatant passenger (piloting excluded).
(c) Letters will subsequently be added after both “A” and “B” for the purpose of indicating limitations of fitness, as follows :—
h....home service (including service in one of H.M. ships based on a home port so long as the ere is not ordered to tropical waters) and service in Western Europe unless the latter is specifically excluded by the medical board.
Unless otherwise indicated an officer will be assumed to be fit for general service"
Para 1446 provided for the same procedures/classes to apply to airman pilots.
Para 1454 provided for airman observers and gunners, to be graded as A3B
Source: 1944 Edn op cit https://archive.org/details/kings-re...ode/2up?q=1434