What is Liquid Water Equivalent (LWE)?

LWE measures how much precipitation is landing.

This is important because real-time precipitation intensity data enables key benefits like More HOTs and Longer HOTs.

Allow us to explain.

A little background info

What is Aircraft Anti-icing Fluid (AAF) and Holdover Time (HOT)?

Aircraft Anti-icing Fluid (AAF) stops ice from building up on planes. Its effectiveness is measured by how long it can keep ice from forming, based on how much precipitation (like snow or freezing rain) it can withstand before it starts freezing or ‘failing’. The failure point is the point where the fluid loses its protective ability and ice starts to form. This necessitates reapplication or additional measures to ensure aircraft safety during winter operations.

Regulators establish Holdover Times (HOTs) by testing the failure times of AAF and publishing HOT look up tables annually. These HOTs indicate how long the pilot has to safely take off before the AAF fails.

What is METAR?

METAR is a globally standardized system for aviation weather reporting. It details current conditions such as temperature, visibility, wind, precipitation, and cloud cover at airports worldwide. METAR reports are published every 30 or 60 minutes depending on the region.

Pilots use METAR weather reports to look up the applicable HOT. While METAR has been a cornerstone of aviation operations since its introduction in 1968, it has certain shortcomings that directly impact HOT determination.

Why METAR is not ideal for HOT determination

Precipitation intensity is critical to determining accurate HOTs. However, METAR does not measure intensity; instead, it uses visibility as a stand-in, which is known to be poorly correlated with intensity. To compensate for this inaccuracy, METAR-determined HOTs are shorter than necessary and can restrict operational capabilities.

If only there were a way to measure the intensity.

In contrast to METAR, LWE measures precipitation intensity, allowing our customers to benefit from More and Longer HOTs.

We operate our LWE HOT service at over 80% of the world’s most winter-intensive airports.

Here are the benefits

More HOTs

METAR-determined HOTs classify +SN as being above 25g/dm2/h and cannot provide HOTs in these cases. This can ground planes causing costly cancellations and delays. LWE, however, is allowed by regulation to provide HOTs up to 50g/dm2/h in snow conditions. This allows for More HOTs which keeps operations running smoothly during heavy snowfall, significantly reducing delays, disruptions and cancellations.

The result is continued operations in heavy weather conditions.

In most situations, when METAR reports ‘No HOT’, LWE provides a HOT.

The results are:

More HOTs available during +SN conditions
Fewer flight cancellations and costly delays due to weather conditions
Planes stay on schedule, reducing airport gate congestion
Smoother and more efficient winter operations, ensuring timely departures despite challenging weather

Longer HOTs

LWE provides precise, real-time data on the exact conditions your airport or aircraft are facing. Unlike METAR, which uses visibility as a rough estimate for intensity, LWE ensures more accurate, tailored HOTs. METAR’s HOTs tend to be more conservative, often overcompensating for actual conditions.

As a result, LWE provides longer, more accurate HOTs tailored to the actual conditions at your location.