I'm trying to avoid "percentage chances".
So in the case you mentioned about flares, I would model how the seeker head is designed to work and let the physics define what happens rather than random numbers.
I agree that for things that the player can detect, or which directly affect mission success, random functions suck.
In some cases, just using the proper physics equations might be simpler and less of a performance hit than look-up tables, random number generators, hit point calculators, etc. In any case, it's more elegant.
The only reason why I suggested random numbers for some systems is that full data might not be available for all systems, it might not be possible to model certain systems with sufficient precision to allow physics models to fully apply (for example, rather than figuring out rate of fuel loss based on tank geometry, bullet size and tumble, tank material, G-forces, aircraft attitude, etc. you could just "hand wave" and assume that a fuel tank will lose rnd * x% of its fuel capacity per second until it slows and stops after rnd * y seconds OR loses rnd x z% of maximum fuel tank volume).
Most importantly, a heck of a lot of what happens in combat is random. Good combat pilots can take full advantage of their plane, environment, and tactical situation, but the law of averages is always waiting to get them. E.g., Bullet tumbles and shatters and it sends fragments of itself and the surrounding material into the engine intake causing progressive engine performance loss due to cascading FOD. Pilot punches out and becomes POW. Bullet doesn't tumble, stays intact, and punches through aluminum/titanium/graphite composite just outside the engine intake with minimal damage. Pilot returns to base blissfully unaware of the angels on his shoulders until his crew chief chews him out for putting a hole in HIS airplane. As Reichsmarschall Manfred Von Richtoften said in an alternate universe, "I'd rather be lucky than good."