There does seem to be confusion but I think there were TWO incidents, both on 22nd, one in August and the other December..../
There is reference in the thread, not only to useful books on the subject of the first heavier than air bombing campaign but
I've got two crewmen killed at Margate on 22 August 1917, there is also :
22 December 1917
On 22 December 1917, when a Gotha from Bogohl 3 crewed by Uffz G Hoffman, Ltn W Döbrick and Vzfw H Klaus approached Westgate a low level. The Gotha had suffered severe engine problems over the English Channel, so the crew jettisoned their bombs and decided to land, which they did at 1800 at Hartsdown Farm near Margate. Ltn Döbrick set fire to the aircraft with a signal cartridge.
The event is mentioned in Volume 5 of The War in the Air and The Air Defence of Great Britain 1914-1918.
At a quarter to six a Gotha attacking England dropped it’s bombs at sea and made a forced landing near the Water Tower, probably south east of Westgate, as its engines seem to have failed. Pilot fired a red light before landing. Pilot set fire to machine after landing and surrendered to the Margate police with two other crew members.
Trust this helps to establish that there were TWO aircraft incidents!