Picture a strip you have flown into a dozen times. From altitude it looks exactly like it always does, a pale ribbon of murram cutting through the bush.
Three days of rain say otherwise, and nothing about the overhead view will tell you that.
The Short Version
- "Wet" is not one condition. A film of water on tarmac, a damp-but-firm unpaved strip, and a saturated murram strip are three different hazards with three different failure modes.
- On paved runways the risk is hydroplaning: your tyres ride on water instead of the surface, and braking and steering both drop toward zero.
- On murram and grass strips the risk is usually not hydroplaning at all. It is lost friction and soft ground that lets a gear leg dig in and the aircraft nose over.
- Most of Kenya's 40 licensed and private aerodromes are unpaved, and most of the private ones have nobody filing a runway condition report. You are the entire assessment system.
- A low pass at a sensible height, read correctly, tells you more than the satellite photo you looked at the night before ever will.
"Wet" is not one condition
Civil aviation has spent the last few years building a formal answer to this exact problem. The International Civil Aviation Organization's Global Reporting Format, in force since November 2021, requires trained assessors to classify a runway surface by contaminant type, depth, and coverage, then assign it a Runway Condition Code from 0 to 6 using a Runway Condition Assessment Matrix, RCAM for short.
The FAA folded the same matrix into AC 91-79B, Aircraft Landing Performance and Runway Excursion Mitigation. It was written primarily for turbine-powered operations with dispatch offices and braking action reports.
You do not have a dispatch office. What you do have is the same underlying question the matrix is trying to answer: is this surface going to behave the way my performance figures assume it will, or not?
The physics that actually catch pilots out
On a paved runway, a thin, continuous film of water can lift your tyres off the surface entirely. This is dynamic hydroplaning, and AC 91-79B gives the classic rule-of-thumb formula for the speed at which it begins: roughly nine times the square root of your tyre pressure in psi.
Run that formula with a typical light-single main tyre pressure and the hydroplaning threshold lands uncomfortably close to normal approach and touchdown speeds, not safely above them. Once hydroplaning starts, braking and directional control both fall toward nil, which is exactly why AC 91-79B spends so much of its length on stopping distance margins rather than technique.
That mechanism needs a reasonably smooth, non-porous surface to work: think Wilson's paved runway, JKIA, Mombasa, Kisumu, or Eldoret after a downpour. It is far less relevant on a porous murram or grass strip, which drains through itself rather than holding a film on top.
Unpaved strips fail a different way. Rain turns laterite clay slick at the surface long before it turns soft underneath, and a wheel that cannot grip steers the aircraft wherever the camber and the ruts want it to go.
Given enough rain, the ground beneath that slick surface softens too, and a gear leg that meets soft ground at speed does not skid, it digs in. The FAA's Airplane Flying Handbook devotes an entire soft-field technique to exactly this failure mode: keep weight off the nosewheel for as long as possible, because a nosewheel that digs into softened ground is how a normal landing roll ends with the aircraft on its back.
It is not only a landing problem
Most pilots think about a soft strip only on the way in, because that is where the accident reports concentrate. The same surface catches you again on departure, and the performance charts in your POH will not warn you about it.
Published takeoff distance figures assume a hard, dry, level surface. AOPA's training guidance is blunt about the gap this leaves: effects the charts do not model, including a soft or grass surface, have to be evaluated by the pilot, not looked up.
A softened murram strip adds rolling resistance the entire length of the ground run, which lengthens your takeoff distance by an amount no chart will quote precisely. Add a full load of fuel and passengers for a safari transfer, and a strip that comfortably cleared your performance margin the week before can quietly stop doing so.
The honest response is to plan every wet-season departure from an unconfirmed strip as if the published figures are optimistic, because for that surface, on that day, they usually are.
The RCAM idea, minus the airline paperwork
You will never file a formal RCAM code before a training flight, and nobody expects you to. What is worth borrowing is the logic underneath it: contaminant type, contaminant depth, and how much of the runway it covers, all assessed before you decide performance figures still apply.
Kenya's own regulatory framework has moved the same direction. The Civil Aviation (Aerodrome Design and Operations) Regulations, 2024 bring Kenya's licensed aerodrome standards in line with ICAO amendments issued since 2013, giving KCAA the regulatory basis to require licensed aerodromes to maintain surface and safety standards rather than leave condition reporting informal.
That regulatory reach covers Kenya's twelve KCAA-licensed aerodromes. It does not extend to the private and concession airstrips that make up the rest of the country's landing surfaces, the ones used constantly for safari and upcountry training flights.
There is no aerodrome operator filing a runway condition report at most of these strips. You are the entire assessment system, every time.
Reading a strip from a low pass
If you cannot get a phone call through to a farm manager, a camp, or a fellow operator who landed there that morning, a low pass is your next-best source of real information, and it is genuinely useful if you fly it correctly. AOPA's guidance on grass-strip operations, built on decades of exactly this problem in the United States, recommends a low pass before committing to land on an unfamiliar or recently rained-on sod strip, specifically to check for standing water, washouts, and long or uneven grass.
Look for specific things, not a general impression. Standing puddles or a visible sheen mean water is sitting on top rather than draining through, which on murram is a strong signal the base beneath it is saturated too.
Grass that is waving unevenly or noticeably longer in patches suggests parts of the strip have not been used, or maintained, recently. Ruts, wheel tracks that look freshly cut rather than compacted, and washouts near the drainage camber all point the same direction: firm in places, soft in others, and you cannot tell which from the air with certainty.
None of that replaces the judgement in crosswind on murram, which covers how camber and surface irregularity change your effective crosswind limit. This is the layer that comes before it: deciding whether the surface supports a normal landing roll at all.
A go or no-go you can actually use
Borrow the RCAM structure without the paperwork. Ask three questions, in order, and let the worst answer govern the decision.
- What is on the surface? Nothing visible and firm underfoot on your last visit is one category. A damp surface with give at the edges is another. Standing water, visible mud, or a sheen across the whole strip is a different category entirely, and it changes the decision, not just the technique.
- How much of the runway does it cover? A soft patch near one threshold that you can avoid by landing long, if length allows, is manageable. A strip that is uniformly soft from end to end is not something technique fixes.
- How old is your information? A dry-looking runway you last confirmed three days ago, after two nights of rain since, is not confirmed. Treat the strip as contaminated until you have current information that says otherwise, not the reverse.
That last habit is the one I would defend hardest. Treating an unconfirmed wet-season strip as contaminated by default costs you a phone call, a low pass, or a diversion to a known-good field.
Treating it as fine by default, because it usually is, costs you the aeroplane on the day it is not. That asymmetry is the whole argument.
Kenya's rain calendar makes this a recurring decision, not a one-off
The Kenya Meteorological Department recognises two main rainfall seasons: the March to May long rains and the October to December short rains, with the whole country affected during both. That is roughly a third of the flying year where an unconfirmed murram strip should be your default assumption, not an occasional caution.
It is not confined to those windows either. A single afternoon convective build-up outside the official rains can soften a strip by the time you fly a second sortie the same day, which is one more reason a runway assessment belongs in your Environment check every flight, not just during the gazetted wet months.
Instructors: put this in the brief, not just the walkaround
A student can execute a flawless soft-field landing and still nose the aircraft over, because soft-field technique manages a known soft surface. It does not manage a surface the student never identified as soft in the first place.
The assessment has to happen before the approach, in the planning and the low pass, not during the flare when options have narrowed to one. Build the three-question check into the pre-flight brief for any strip outside the paved network, and revisit it verbally on the downwind leg if the strip has not been used in the last day or two.
A Certified Flight Instructor who only checks technique on the ground has covered half the risk. The other half is the judgement call about whether to attempt the landing at all, and that call needs to be taught explicitly, not assumed to develop on its own.
What pilots admit on the forums
Grass and bush-strip forums have a recognisable pattern whenever a wet-season nose-over comes up. Almost nobody claims the runway looked bad from the air.
The recurring admission is the opposite: it looked completely normal, the same colour and shape it always was, and the softness only became obvious once the wheels were already committed and slowing was no longer optional. Several threads independently land on the same fix, which is treating a recent-rain strip as guilty until a fresh, on-the-ground source clears it, rather than trusting a photograph or a memory of how the strip usually behaves.
That is not a dramatic insight. It is the same discipline the RCAM framework enforces formally at big airports, arrived at independently by pilots who learned it the expensive way.
AngaBrief's Environment section asks for a surface-condition entry on every pre-flight assessment for exactly this reason, so a soft or unconfirmed strip gets flagged before departure rather than discovered on rollout.
The tool records the assessment. The go or no-go decision stays with the pilot in command and the assigned instructor, always.
Key Takeaways
- Wet tarmac risks hydroplaning; wet murram and grass usually risk lost friction and soft ground instead. Know which one applies to the strip in front of you.
- Borrow the RCAM logic without the paperwork: what is on the surface, how much of the runway it covers, and how old your information is.
- Most of Kenya's unpaved strips have no formal condition report. A recent phone call or a correctly flown low pass is the only reliable substitute.
- Treat an unconfirmed wet-season strip as contaminated by default. The cost of being wrong in that direction is a diversion, not an aeroplane on its back.