My longest flight with 99 Sqn was on Britannia XM 520 from Edmonton (Alberta, Canada) to Lyneham. My logbook shows it took place on 17-18th June 1962 and took 12 hours, 10 minutes for the non-stop flight. Distance flown around 4,300 Great Circle miles I think.
Mind you at Seletar a couple of years earlier Flt. Lt. N. Bull (Norman Bull?) of 205/209 Sqn. flew a dedicated endurance flight from Seletar on 18/19th February 1958 with a Sunderland that was airborne for 20 hours 30 minutes. I left Seletar on posting in January 1958 so wasn’t present when this flight took place, but it was fairly common knowledge in FEAF.
Not sure if this was a record or not, but many years later whilst researching in the National Archives at Kew had a look at 205/209 ORB for the relevant dates and sure enough the squadron ORB records the following:
Aircraft. Sunderland ‘R’ RN303
Captain. Flt. Lt. N. Bull.
Airborne. 18th February 1958 at 14.55
Down. 19th February 1958 at 11.25
Mission. “NAVEX and Endurance Flight”