There are two competing perspectives here.....
HBA1c is a measure of long(er) term control. With BP, lipid and lifestyle control, it's essential for living a longer and healthy life. It's a video of the train.
Plasma glucose level is probably more relevant to a diabetic pilot who is about to pilot his passengers about......but generally only if he or she is at risk of having a hypoglycaemic attack, and thus rendering him suddenly incapable. This is usually only the case when a pilot is actually taking a medicine that would cause this.
Plasma glucose level (the usual "fingerprick" machines), take a snap shot of the train. It show's where the train is now. It doesn't show where it's been, where it's going, or how fast it's getting there.