Anonymity?
Ask yourself this - Why has each pilot been issued with a unique identifier for their survey?
Under the guise of ensuring only one filled out per individual?
De-identified? Not a chance. There will be a tracking pixel in the html coding of this survey, and each result will be checked against the individual.
To assume anonymity is to not understand Cx.
You do this survey, you may as well have written your name in texta across the top.
Sure as night follows day.