I had a fleet of Vickers Viscount and Vickers Super VC 10 cargo; all Viscounts worked perfectly throughout the crisis, and I had to downsize fleet of VC10s, got rid of all unprofitable routes, and the remainder, ~20-25 frames, got me through. Their profit was down from ~500-600 kUSD per week to like ~200 k per week.
Similar in AG, there was fuel crisis around 2010 or so - check all routes and planes and ditch unprofitable ones to save the healthy ones, and if possible switch timely to more efficient planes, as simple as that, no other way, I think. Once the crisis is over, rebuild the fleet, and during crisis keep the eye on notable bankruptcies, to catch demand left after them if possible.