As an aircraft Commander (UK airline), I'm afraid I have NO discretion whatsoever as to allowing an ATC'er entry to the flight deck during flight, unless it is pre authorised through management in advance.
There are since 9/11 far more stringent checks and processes to pass through to get you on the Flt deck, none of which can be dealt with from an ad hoc request 'on the day'.
Even if you bring your pass/license I can't let you in unless you have sorted it all in advance, and my company have advised me of your authorisation. Sorry........ anything other than that will now fall under wilfull and gross neglect of security procedures by myself and lead to disciplinary action - possibly dismissal!
For what it's worth I have always believed there is great value to having ATC'ers come on fam flts, likewise pilots getting themselves inside ATC facilities and understanding ATC's problems and niggles.
I have carried many fam flts over the years, including 2 from my local unit in the last week. I made the applications on their behalf after requests from the unit, activated and chased the admin now required - all hassle, time consuming, but I do believe worthwhile.
In summary,yes Fam Flts are available, but please please sort well in advance to avoid dissapointment on the day - we no longer have discretion to open the door to you whatever your proven credentials!
30W