RaM, I wouldn't doubt it. In the case of an emergency I would imagine planes might need to dump fuel both to lighten their load and to reduce the risk of fire in a crash. ...
Correct - on both counts, with respect to emergency landings ...
However, the 'load / weight factor' applies to non-emergency landings as well. Here's why ...
Landings are rough, and aircraft are designed to safely land with up to a certain maximum weight on board. Every aircraft type has detailed specifications for the relevant parameters, and these specifications are in play during flight planning.
There's a big problem, though ... One thing that can easily turn a safe landing into a runway crash is having the onboard weight shift. Cargo palettes and passengers are tied down / belted in, and don't shift. Liquids - such as the possibly thousands of pounds of avgas in a plane's fuel tanks - slosh around. To make matters worse the sloshing fuel is typically housed in the wings - the components most vulnerable to load-related stresses.
Aircraft fuel tanks (typically bladders nowadays) are equipped with baffles and other things to minimize such sloshing, but there's frankly no way to reasonably ensure a fuel load won't or can't slosh around.
As a result, there are strict specifications for how much fuel load a large aircraft can safely carry when landing.
For most routine cases (e.g., commercial airliners) this landing fuel weight constraint is baked into the planning, so that jettisoning fuel becomes necessary only when the aircraft has to land earlier than expected.
The
really critical situation has to do with tankers. If a tanker lifts off with, say, 100,000 lbs. of fuel intended to be offloaded to other aircraft, more than 90% of that weight can't simply be brought back to terra firma again. It has to be burned up by the tanker itself, offloaded to the intended or other recipients, or ...
The in-house term for the last-ditch solution is 'weight adjustment'. Major weight adjustments are (thankfully ... ) rare, and whenever possible tankers are diverted to remote locations (e.g., over the ocean) to perform them. Any such weight adjustments are performed at higher altitudes to dissipate the dump.
Just so we're clear ... No - the chemtrails BS isn't attributable to profligate fuel-related weight adjustments.