Three documented gaps between what an in-cockpit weather display shows and what the atmosphere is actually doing. Every one of them is in a public government document. Every one of them has a source you can go and read.
What this page is not. It is not a claim that anyone is hiding anything, and it is not a conspiracy. These are engineering limits and editorial choices that were each defensible on their own, documented in public, and which combine into something a pilot is never shown in one place. That last part is the failure.
This is the most serious of the three, because it is the one where the display is actively confident about something wrong.
When NEXRAD weather reaches your cockpit over FIS-B or satellite, it arrives as a mosaic stitched from many ground radar sites. The clock on your display is the age of the mosaic, not the age of the weather in it. The NTSB put it in bold in Safety Alert SA-017:
“The age indicator associated with the mosaic image on the cockpit display does not show the age of the actual weather conditions as detected by the NEXRAD network. Instead, the age indicator displays the age of the mosaic image created by the service provider. Weather conditions depicted on the mosaic image will ALWAYS be older than the age indicated on the display.”
NTSB Safety Alert SA-017, In-Cockpit NEXRAD Mosaic Imagery, June 2012, revised December 2015. Emphasis is the NTSB’s, not ours.
How much older? The NTSB says the actual age of the oldest data in the mosaic can exceed the indicated age by 15 to 20 minutes. A cell moving at 30 knots travels ten miles in twenty minutes. The gap you are threading may have closed before you were told it existed.
The display said the image was about 1 minute old. The conditions in it were about 5 minutes old. It showed severe weather roughly seven miles from the home base he was trying to land at. The severe weather was crossing over that base at about the moment the image arrived.
He was diverting around weather and doing it correctly — per the NEXRAD data he received, he would have been clear of the precipitation. His last three updates each reported themselves as 1 minute old. They were actually about 6, 7 and almost 8 minutes old. He flew into a developing shower his display still showed him clear of.
Both cases are drawn from SA-017 itself, which cites the NTSB case numbers and dockets above. Neither pilot ignored the weather. Both were using the equipment the way it is taught, reading a number that was accurate about the wrong thing.
And here is the institutional part, in the NTSB’s own
words: latency “is discussed in pilots’ guides, in industry literature, and on
service providers’ websites. However, the NTSB has not found that such guidance
contains details about the potential time difference between the age indicator and
actual conditions.”
The warning exists. The number that kills you is left out of it.
A sea-breeze front shows on raw radar as a fine line — a thin arc of clear-air return, typically 5 to 20 dBZ, that appears before the first cumulus does. It is the earliest observable signal that storms are coming and where.
Datalink weather encodes reflectivity into coarse bins and the lowest of them starts well above that, so the single most useful early signal in a Florida afternoon is, structurally, not in the product. Not filtered by accident — simply never sent. The floors are tabulated on the front page →
On that number, honestly. The figure usually quoted for the FIS-B floor is 20 dBZ, and it is repeated widely. I could not confirm it against the FAA’s own service specification (FAA-E-3006), so it is not stated here as though I had. If you have the primary citation, send it and this paragraph gets replaced by the number and the page it came from.
But look what happens when you go looking for it. The FAA publishes a 539-page Aviation Weather Handbook for exactly this audience. Search it for the reflectivity floor of the datalink weather the FAA itself broadcasts into your cockpit and you will not find one: “FIS-B” and “dBZ” appear together on exactly one page, and it is the list of abbreviations.
So a pilot cannot look this up. Not because the answer is secret, but because the document written to teach them weather never connects the product they are using to the sensitivity it has. That gap is checkable, and it is the point.
The FAA’s own Aviation Weather Handbook covers this class of return in Chapter 15, section 15.2.12, under the heading “Angels”, inside a run of subsections on non-meteorological phenomena. Verbatim:
“Angels are echoes caused by a physical phenomenon not discernible by the eye at the radar site. They are usually caused by bats, birds, or insects. Angels typically appear as a donut-shaped echo with low reflectivity values... Angels typically only appear when the WSR-88D radar is in Clear Air Mode because of their weak reflectivity.”
FAA-H-8083-28A, Aviation Weather Handbook, §15.2.12. Checked against the FAA’s published PDF, all 539 pages.
That attribution is not wrong. Clear-air return genuinely is often insects lofted by the convergence. But the reason the insects are up there is the convergence, and the convergence is the thing that is about to build a thunderstorm. Read it again and the handbook has already told you the mechanism — weak returns, visible only in clear-air mode — and then filed it under things to disregard. It teaches the signal’s cause and discards its meaning.
And the term that would let a pilot look this up? The phrase “fine line” appears zero times in the entire handbook. That is not a figure of speech; I searched all 539 pages of the published PDF. There is no entry to find.
Not for navigation, and not a substitute for a briefing. This is training material built by a private pilot, not an instructor, an examiner or a meteorologist. Sources are linked so you can check every claim on this page, and you should.