It’s become rather predictable. Government pronouncements claim that because the national unemployment rate is down to around 5%, it means that the U.S. economy is humming along.

But in fact, that conclusion doesn’t square neatly with the reality that the unemployment percentage is calculated based on the lowest level of workplace participation in decades.

So, which is it?  A strong economic upturn … or a middling recovery?  When the average citizen is the judge rather than breathless PR flacks, it’s the latter.

The same could be said about the airlines.

The amount of “happy-talk” about passenger airline travel is quite high these days.  Some of the news is undoubtedly welcome:  The lowest jet fuel prices in recent memory are making it cheaper to fly cross-country today than in years.

But upon further scrutiny, another spate of good news seems to be little more than blue smoke and mirrors. For a number of years now, the passenger airlines have been crowing about their on-time flight arrival performance.

The statistics purport to show that on-time performance rates for commercial airlines have been steadily improving.

But look a little closer … and the skies aren’t quite as clear-blue as all that.

A study by OAG Aviation Worldwide, a UK-based analytical firm that analyzes travel data, finds that airlines have been padding their flight-time schedules going on 20 years now.

Here’s a representative example of what’s been happening:  OAG evaluated 1,400+ commercial flights scheduled between Los Angeles International Airport and San Francisco International Airport.  Back in 1996, not even one of the flights between these two airports was scheduled to take longer than 90 minutes.

And yet … by 2015 the airlines had allotted flight times of between 91 and 110 minutes for nearly half of the flights scheduled between those two airports.

Of course, it’s axiomatic that if the scheduled flight times are lengthened upwards of 10%, that will take a so-so on-time flight arrival statistic and transform it overnight into a pretty impressive one.

… And the transformation’s been accomplished without changing a thing where it actually counts: on the ground (or in the air, I could say).

For the record, no one at the airlines is acknowledging this statistical sleight-of-hand. Asked to comment on the OAG study’s findings, a spokesperson for the trade group Airlines for America (A4A) responded with this rather mealy-mouthed statement:

“We have the same goals as our customers, which is to get them, their luggage and packages to their destination safety and on time.”

Well, at least they’re not fudging on the safety part …