If you read the ruling (find it here), you'll see that the DOT looked at the exemption requests and weighed various options, from providing an exemption just at JFK, to the entire NYC-area airspace, to also including Philadelphia -- all pertaining the the various airline requests received in the past few months.

They found no persuasive argument for granting the exemption, based on two conclusions. One I find valid, the other I find not so much.

1) Passengers have rights: The origins of the tarmac rule are passenger rights to not be "held hostage" on a plane for more than 3-hours without taking off. This fundamental truth does not change just because the Port Authority is doing construction at JFK. In my own discussion on this, I stated this as the primary rationale for not granting the exemptions. If the rule makes sense normally, why wouldn't it make sense now? If anything, it should make MORE sense now since these are the times when it's most likely to happen. Exempting airlines from the rule when it's most likely to come into play is ridiculous. Kudos to the DOT for recognizing this and holding firm!

2) DOT has the right to apply penalties with discretion: Woah! This is the DOT saying that they won't exempt airlines from the rule, but if a 3+ hour tarmac delay occurs during some pretty gnarly circumstances at these airports, well, they can always opt not to fine the airline (or fine them very little). This is true, as it's built into the text of the original rule. The maximum fine is $27,500 per passenger, but in subsequent clarification, the DOT has said that they would rarely fine the max amount.

Let me pose a question: What's the point of policy if its enforcement is wrapped up discretion? Yes, this is a common thing in all policies, civil and criminal alike (ever heard of prosecutorial discretion? folks live and die by this stuff).  But for airlines, the max fine is significant enough to cancel a flight and they have to calculate the cost/benefit risk analysis of violating it in order to make those decisions. That analysis requires the fine as an input. So how can airlines do that if it's a discretionary fine?

Over time, the DOT will establish a precedent of how much airlines get fined for what sort of behavior. In the beginning, airlines will likely have to assume close to max penalty for their analysis so they don't get housed.

In the meantime, the DOT is telling the airlines that they'll penalize based on how poorly the airline behaves rather than the circumstances that are beyond their control. That's reminiscent of the Supreme Court ruling on obscenity -- the infamous "i'll know it when I see it" quip From Justice Potter Stewart in 1964. That's quite the "policy" when millions of dollars and passengers' lives are at stake.

Come April 29 when the rule goes into effect, we'll all get to see exactly what that means. Both how the airlines plan for it and how the DOT responds. I might try to avoid JFK during those first couple of weeks until things settle out (oops, flying into JFK myself on May 6).

In the meantime, congrats to the DOT for throwing down with the airlines. Nice to remind them who's boss every now and then. At least until their lobbying group has you removed you from office.