The charity was called to assist the crew on PBY Catalina on Saturday after they experienced engine trouble while attempting to take off from the loch.
The lifeboat was contacted at 5.50pm to assist the plane, which was drifting in the middle of the loch.
RNLI volunteer crew made the decision to tow the plane to Urquhart Bay for safety.
With a wingspan of 32 metres, the Second World War seaplane was too wide to recover to a harbour or pontoon, so a mooring buoy was decided as the best option.
Lifeboat crew member David Ferguson said it was a challenge to tow something as big and unusual as the aircraft.
Mr Ferguson said: “Towing the Catalina would prove to be no easy feat.
“Fixing points are few and far between on such an aircraft, and the best option was underneath the tail, which barely cleared the bow of the lifeboat.
“Nevertheless, with some care, we managed to establish a towline.”
With dark quickly falling, the tow was a slow process. Searchlights were used to keep track of the mooring buoy, located near Borlum Pier.
Once the seaplane was secured, the four crew onboard could safely disembark the aircraft.
The lifeboat then escorted the crew across the bay to their colleagues at the harbour and returned to the station.