Page 250 "
Reminiscenes of the Russian Revolution" by M Philips Price who was in Petrograd at this time has on 27 Feb 1918:
"During the afternoon a German Aeroplane flew over from Pskoff and dropped 2 bombs on the Fontanka Embankment"
Pleskau/Pskow/Pskov the Germans captured on 25 Feb 18 from a map from der Weltkrieg. This is where the Tsar abdicated in march 1917.
Fontanka 16 is where the Corps of Gendarmes HQ was until it was sacked and burned during the March 1917 revolution
other sources list the first bombing raid on Petrograd on 2 or 3 march 1918
RMAF map has Pskov around 140 miles from Petrograd
on 4.3.18 with the German 8th army in Kurland are FA 8, 22, 37 and FAA 214
i hope this is of some interest or use