More common than expected: How standing water impacts airport safety and operations

In 2021, ICAO introduced the Global Reporting Format (GRF) for Runway Condition Reporting (RCR). Runway condition reporting isn’t new – when runway conditions change, airports monitor, record and report the changes – but it typically requires manual inspections by staff and downtime for runway operations.

The aim of ICAO’s GRF is to standardize reporting globally, in the hope of reducing the 25% of all aircraft accidents that come as a result of runway excursions.

Although winter weather gets a lot of attention for changing runway conditions; globally, rain is the most frequent cause of a change in runway condition. And within that, standing water is more common than expected even in the mildest climates.

What is standing water?

On the list of things that can impact airport operations day-to-day, standing water on a runway may not seem like the most important – especially in moderate climates. But our research at NACO paints a very different picture – with standing water occurring more frequently than expected, even in the mildest climates.

But what exactly is standing water? When rain falls it builds up to form a water film on the runway. The depth of this water film has big impact on aircraft performance. Within the new GRF, it must be reported as follows:

> If the water film depth is 3 mm or less, the runway is considered wet, which must be reported via the RCR with a runway condition code 5.

> When the water depth exceeds 3 mm, standing water must be reported by changing the runway condition code from 5 to 2.

> Water films exceeding 3 mm can cause aircraft to experience aquaplaning, which poses a serious threat during take-offs and landing.

Why is standing water more common than expected?

Many airports do not expect to experience standing water. It’s believed that very high rainfall intensities (in excess of 100 mm/hr) are needed for this to occur and these intensities are not regularly expected.

But it’s not quite that simple. The regular meteorological data taken from an automated weather observing system (AWOS) for example, suggests that significant rainfall intensities do not occur commonly. However, these types of meteorological stations report rainfall intensities in 10 or 15-minute intervals.

Given the dynamic character of water, this interval is too long to detect standing water on a runway.

We extensively measured rainfall intensities and found that – while 10-minute and 5-minute reporting intervals suggest there is no risk of standing water – if reported in 1-minute intervals, the peak intensity does regularly exceed 100 mm/hr, which is likely to lead to standing water.

With the increase in heavy showers, even airports in moderate climates should realize that standing water on their runways is a realistic condition. Even though standing water may only occur for a short period of time, the (unexpected) impact on an aircraft, landing or departing, will be significant.

What makes reporting standing water so difficult?

With conditions like standing water occurring more commonly than expected, airports should conduct regular assessments of water depths during heavy rains. But assessing the condition can be challenging work:

> Assessments must be conducted on the runway in between aircraft movements – reducing runway capacity.

> Runway inspections during adverse weather conditions can put inspectors in unsafe situations.

> 1 mm of difference in water depth can have a significant impact on aircraft braking and take-off performance – making accurate reporting essential.

> Significant changes in conditions can occur within minutes which means that by the time a manual assessment is finished, your report can be outdated already. This could cause the information received by pilots to not reflect the actual condition the aircraft will experience.

The good news is that almost all of these challenges can be eliminated by automating both the runway assessment and reporting process.

That’s what we’ve done at NACO with our RCR-Tool© – enabling accurate runway condition assessments and the ability to disseminate the RCR in real-time, eliminating the need for runway occupancy by inspectors.

The RCR-Tool© is constantly monitoring the runway condition and recognizing significant changes immediately airports do not have to rely on inspectors to notice a change, and can issue an accurate report in seconds.

You can download our White Paper on standing water and its impact https://www.naco.nl/expertise/asset-optimisation-airport-systems-and-operations/rcr-tool?utm_source=ACI+blog&utm_medium=referral&utm_campaign=RCR#whitepaper