NTSB Targets Wet-Runway Braking: Three RCAM Recommendations Land on the FAA's Desk

On May 12, 2026, the National Transportation Safety Board released Aviation Investigation Report AIR-26-04, Accounting for the Progressive Decrease in Runway Friction Associated with Increasing Rainfall Intensity, formally transmitting three safety recommendations to the FAA in a May 26 letter from Chairwoman Jennifer Homendy. For those of us who compute and verify landing performance every day, this one hits close to home: the central finding is that the friction numbers we rely on for wet runways may be optimistic, and the weather data we use to flag the problem may not be granular enough to catch it.

What the NTSB Looked At

The recommendations stem from NTSB analysis of 11 wet-runway overrun accidents and incidents over a 15-year span (2008–2022). Using a flight-data technique the Board first developed after the 2008 Owatonna, Minnesota, BAe 125 accident, investigators back-calculated the actual wheel braking friction coefficient achieved on each landing and compared it to what the FAA's Runway Condition Assessment Matrix (RCAM) would have predicted.

The result that should get a dispatcher's attention: in all but one of those 11 events, the friction the aircraft actually achieved was substantially lower than what the RCAM assigns to a wet runway (runway condition code 5). In nine of the eleven, the shortfall was most likely driven by moderate-to-heavy rainfall and the resulting water depth. Low runway friction was cited as causal or contributing in eight.

The Core Problem for Performance Planning

Two technical issues underlie the recommendations, and both bear directly on the landing distance assessments we and our crews perform:

1. The friction floor for "wet" is too high. A runway coded 5 ("good" braking, wet, up to 1/8-inch water) derives its friction from the method in 14 CFR 25.109(c). That method accounts for groundspeed and tire pressure, but not for water depth, surface texture, rubber deposits, tire wear, or temperature. The RCAM treats the transition from a wet runway (code 5) to a flooded one (code 2) as a sudden jump once water exceeds 1/8 inch. In reality, the NTSB argues, friction degrades progressively as rainfall — and water depth — increase. There's no smooth path between code 5 and code 2 in today's matrix, even though the physics is continuous.
2. We default to code 5, and we usually have no reason not to. Here's the operational reality the report names directly: water depth on runways is generally not measured, most airports serving turbine traffic have no continuous friction measuring equipment, and "slippery when wet" designations are rare. Without a braking action report from a preceding aircraft, operators and crews will assume code 5 by default. In every one of the 11 overruns, the flight crews had nothing prompting them to run their numbers against anything worse than wet — even though lower codes would have been more representative of the actual runway.
3. "Heavy rain" can't tell you how heavy. This is the piece dispatchers should flag hardest. The most intense rainfall descriptor available in aviation weather reporting is "heavy," defined as anything greater than 0.30 inches per hour. But in six of the overruns, rainfall was 1.3 to 20 times that threshold. At Jacksonville in 2019 (the Miami Air 737-800 that ran off Runway 10 at NAS Jacksonville into the St. Johns River), rates were 0.6–2.4 in/hr — 2 to 8 times threshold. At Sugar Land, Texas, in 2016, rates hit 4.2–6.0 in/hr — 14 to 20 times threshold. A METAR or TAF reading "+RA" gives the crew no way to distinguish a 0.3 in/hr event from a 6.0 in/hr deluge, even though the friction and required landing distance differ dramatically.

The Three Recommendations

A-26-61 — Update the RCAM runway condition codes assigned to wet runways to account for the progressive decrease in the wheel braking friction coefficient as rainfall intensity increases. (The NTSB notes any update should distinguish grooved from smooth runways, since grooving drains water and preserves friction; a proposed method is on page 11 of the report.)

A-26-62 — Add new rainfall intensity descriptors to aviation weather reports to identify rainfall that can substantially exceed the current 0.3 in/hr heavy-rain threshold. The report illustrates possible descriptors like "heavy+," "heavy++," and "heavy+++" tied to escalating rate bands.

A-26-63 — Once those new descriptors exist (per A-26-62), incorporate them into the RCAM so that higher rainfall intensities map to progressively lower runway condition codes.

The report includes an illustrative table linking rainfall bands to condition codes — for example, 0.5–1.0 in/hr ("heavy+") to code 2, and above 2.0 in/hr to code 0 (no operations). The Board stresses this is for illustration only.

What This Means — and What It Doesn't

It's worth being precise about the regulatory status here. NTSB recommendations are exactly that: recommendations. The NTSB investigates and advises; it has no rulemaking authority. The FAA will review AIR-26-04, evaluate the three recommendations, and make its own regulatory determinations — which could range from full adoption through advisory circular or rulemaking, to alternative action, to a reasoned decision not to act. The NTSB has asked the FAA to respond within 90 days of the May 26 letter describing intended actions. Any actual change to the RCAM, to AC 25-32 / AC 91-79B, or to weather-reporting descriptors in the Federal Meteorological Handbook No. 1 would follow the FAA's own process and timeline. Nothing changes in your performance calculations today.

That said, the operational takeaway needs no rulemaking to be useful now: when heavy rain is in the picture, the assumption that a wet runway equals code 5 / "good" braking deserves scrutiny, and time-of-arrival landing distance assessments under AC 91-79B remain the dispatcher's and crew's best tool for building margin.

Airline Dispatchers Federation

The Airline Dispatchers Federation will continue to monitor the FAA's review of these recommendations and stands ready to provide subject-matter experts to the agency when appropriate. Dispatchers sit at the intersection of weather interpretation and performance planning that these recommendations address, and the dispatch community's operational perspective is directly relevant to how any RCAM or weather-descriptor changes are ultimately implemented.