JohnBurke

A review of your medical certificate, on the back of the certificate, will note the conditions of issue, which include to "comply with the standards relating to prohibitions on operation during medical deficiency (14 CFR 61.53, 63.19, and 65.49).

14 CFR 61.53 states (emphasis is mine):

https://www.ecfr.gov/current/title-1.../section-61.53

The back of the medical certificate, Form 8500-9, also states that a condition of issue is that one will "comply with validity standards specified for first, second, and third class medical certificates (14 CFR 61.23).

14 CFR 61.23 sets the requirement to hold a medical certificate, and which level of medical certification privilege is required (eg, 1st, 2nd, or 3rd class, as well as basic med and use of a driver license in lieu of a medical certificate for certain operations).

The latter, use of a driver license in lieu of a medical certificate, is of interest, in part because it requires that one has demonstrated the ability to get a FAA medical certificate, and also because one cannot have any condition that would prevent issuance, and one's most recent application has not been denied or would not have prevented one from obtaining a FAA medical certificate. This is of interest here because these same standards apply to holding your first class medical, including the question at hand in this thread, regarding holding a medical, but an issue with the most recent application.

As previously noted, if you have any condition that would prevent issuance (including delaying or deferring it), regardless of whether you are initiating a new application, then you're not medically fit to hold the certificate and cannot exercise the privilege of the certificate for the duration of the period that you have that condition, or until that condition is resolved. If you take a medication that impairs you in any way, for example, while that medication has effect, you are not medically qualified to exercise the privileges of your medical certificate (and by default, your pilot certificate, so long as it requires you to hold medical certification). This is the case with all FAA certification; even the airworthiness certificate for an aircraft states on the back of the certificate the conditions for which it is issued, and includes a clear statement that the aircraft is not airworthy, so long as it does not meet its certification standard (type certificate data sheet, for example, and any amendments thereto). Just as an airplane isn't airworthy if it doesn't meet its certification standard, you're not airworthy if you don't meet your pilot or medical certification standard, even if only temporarily, and even if you still hold a paper certificate that says you're qualified. The paper qualification is invalidated until you fully meet the standard once again. You can have alcohol, but until it's passed from your system, you are not medically fit to fly and your paper medical certificate does not make you fit.

Looking at the basic med and use of a driver license in lieu of a medical certificate, we can see a statement that bears a closer look: the applicant must have been found eligible to hold at least a third class medical certificate at the time of his or her most recent application. This could have been ten years ago, this most recent application, but the intent is clear: the applicant must have previously held a medical and it can't have been denied. This thread isn't asking about basic med or the use of a driver license or a third class medical, so how does this possibly apply? The standard is the same: you can't operate if you've been denied a medical, or if you have a condition that would prevent you from holding one.

This brings us to bear on the pivotal question of the thread: what if it's a condition that's been deferred; sent for further consideration (but hasn't been denied)? A FAA Chief Legal Counsel letter of interpretation can be read to gain some insight into that. The letter is written to cover a question about basic med and the driver license, but addresses the most recent medical application, and it is that portion of the interpretation that is significant here. Let's look at it:

In March 28, 2007 Chief Counsel letter of interpretation from Rebecca MacPherson to Frederick Tilton (Federal Air Surgeon), the issue was addressed of an airman who wanted to use his driver license in lieu of a medical certificate, but had previously been denied a medical application. The applicants argument was novel: under the regulation, failure to contest a denial after 30 days is considered a withdrawal of the application. The applicant chose not to contest the denial, and after thirty days, his application was thus considered withdrawn. His argument, then, was that he couldn't be disallowed from using his driver license as a medical, if his previous medical application had been withdrawn. The chief legal counsel saw it differently (and consequently, so must we, as this represents the position of the FAA Administrator here). Quoted in part:

https://www.faa.gov/sites/faa.gov/fi...rpretation.pdf