My transponder is out of compliance as it has not been tested per 91.413(a) in the preceding 24 months. The airplane is otherwise airworthy, and I need to fly it to a maintenance facility to get the testing done. Per 91.413(a) I understand that I can't “use” the transponder. 91.215(d) describes “ATC authorized deviations” from transponder use requirements. 91.215(d)(2) seems to fit the bill, and it says the request “can be made at any time.” Trying to understand how this works: Can I depart VFR (non-towered airport), call up approach and request authorization to proceed to the repair facility with the transponder in standby, or do I need to phone first and get some sort of pre-authorization? My destination is a towered airport (Class D).
You are correct about the regulation in that the request in your case can be made “at any time.” It can also be denied at that time. So you stand a good chance of showing up and being told, “Sorry, too busy for no-transponder airspace entry.”
If you were flying into transponder-required airspace I would recommend calling ahead to clear it ahead of time, especially since as from 1/1/20 transponder-required airspace is also ADS-B-required airspace, and the protocol for no-ADS-B operations in ADS-B-required airspace involves doing the ADAPT request/approval before flight.
However, if you're not going through any transponder-required airspace, you can just leave the transponder in STBY/OFF and go.
The airplane has ADS-B out and in.
It is completely illegal to operate with that expired transponder on anywhere in the US National Airspace System. That is explicitly stated in 91.413(a), and ATC has no authority to waive that regulation.
Also, some ADS-B-out systems rely on the transponder for operation. If yours is such, then operating within the Mode C veil of Class B airspace with the transponder off would violate 91.225(d)(2) unless you obtain approval for-ADS-B-out inoperative operation IAW 91.225(g)(1). As stated above, while such a request may be made “at any time,” it may be denied, leaving you stuck outside the airspace. Best to phone ahead.
ARTCC ("Center“) can't help. For Class B airspace and the Mode C veil around it, you must contact the TRACON ("Approach”) which owns that Class B airspace. Phone numbers are in the airport entries in the A/FD section of the Chart Supplement. Might not be in towered airport entries, so you may need to look at the entry for a nontowered airport under or near the Bravo.
Please correct me here, but a transponder is only require in Class C, 30 mile radius of Class B, and above 10 feet(lower 48). So a transponder is not required to fly to a Class D airport. If I remember correctly, the regulations say it cannot be turned on if current inspection has not been completed.
§ 91.215 ATC transponder and altitude reporting equipment and use.
§ 91.413 ATC transponder tests and inspections.