Holdover time is calculated
from three measurements you have to trust
Environmental measurement for de-icing decisions and holdover times, with heated ultrasonic wind sensing and optical precipitation measurement that keeps reporting through the conditions it exists to describe.
Winter costs the airfield either way
De-icing fluid is expensive, and applying more of it than the conditions require is a cost repeated on every movement through a whole season. Applying less than they require is not a cost, it is an occurrence.
Between those two sits holdover time, which is calculated from temperature, humidity and the type and rate of precipitation falling at the time. Get those three right and the airfield keeps its movement rate through weather that would otherwise stop it.
The difficulty is that the measurement has to be made in exactly the conditions that defeat instruments. A tipping bucket fills with snow, a mechanical anemometer ices and quietly reports calm, and a screen reading taken from the wrong part of the field describes somewhere else.
Every airfield decision starts at a measurement point
An airport measures across the whole estate. Surface wind along the runway. Temperature, humidity and precipitation for approach and de-icing. Heat stress and machinery condition on the apron.
Runway threshold and touchdown zone
Surface wind at the threshold is the number the crew acts on, and it is reported continuously whether or not anyone can reach the mast.
- WindObserver 70 FAA and CAA accepted for AWOS use, heated head, 0 to 70 m/s
- WindObserver 75 316 stainless open head where site winds run higher
- WindSonic 60 lighter 2-axis for a secondary reference
Runway midpoint reporting
Wind can differ along the length of a runway, so mid-point sensors give the tower a truer picture than a single threshold reading.
- WindObserver 70 1 to 4 Hz output, RS422 and RS485
- WindSonic 75 0 to 75 m/s, 0.5 kg, low-cost additional reporting point
- MetConnect THP adds temperature, humidity and pressure at the same location
Runway stop-end and secondary masts
Stop-end and secondary masts fill in the picture the threshold sensor cannot see, and they sit where access needs a runway closure.
- WindObserver 70 no moving parts to seize between inspections
- WindObserver 90 0 to 90 m/s where exposure demands the wider range
- WindSonic M heated aluminium body, operating to -40 degrees C
Approach and departure path
Approach decisions depend on wind, visibility and precipitation reported from the ground, at the rate the procedure needs.
- WindObserver 70 the model that carries FAA and CAA acceptance
- MaxiMet GMX501 wind, temperature, humidity, pressure and solar in one unit
- TruMet PW100 optical rainfall, 0 to 200 mm/hr, no moving parts
Control tower and ATIS reference
The tower display and the automated broadcast both trace back to one set of sensors, so the output format matters as much as the accuracy.
- WindObserver 70 RS422 and RS485, full or half duplex, 1200 to 38400 baud
- MetConnect One ASCII, Modbus RTU and ASCII, NMEA 0183 and SDI-12 v1.3
- MetConnect THP pairs with a heated remote anemometer for cold sites
AWOS and automatic weather station enclosure
The field station is where the parameters come together, and WMO siting wants them separated by height rather than stacked in one housing.
- MetConnect THP separates sensors by height, accepts Pt100 and analogue inputs
- WindObserver 70 the remote anemometer feeding the station
- TruMet PW100 contact-closure rainfall input, 0.1 mm resolution
Airfield wind reference and sensor siting
A wind sensor is only as good as where it sits. Obstructions, buildings and mast height all change what the instrument reports.
- WindObserver 75 open head holds accuracy as the flow angle increases
- WindSonic 60 0 to 360 degrees with no dead band
- MetConnect One integrated WindSonic with T, H and P in one hub
Helipad and HEMS operations
Rotary wing operations turn round fast and often at night, and the wind limit is checked at the pad rather than the main met station.
- WindObserver 70 heated, IP66, 316 stainless, icing tested to MIL-STD-810F
- MaxiMet GMX501 compact station where pad space and cabling are tight
- WindSonic M heated, 0.9 kg, for a lightweight pad-side reference
De-icing pad and winter operations
De-icing is scheduled against temperature, humidity and precipitation, and the holdover time depends on getting those three right.
- MetConnect THP temperature to 0.2 degrees C, humidity to 1.5 percent RH
- MaxiMet GMX550 wind, T, H, P and rainfall, optional heating to -40 degrees C
- WindSonic M heated wind sensor for the pad itself
Aircraft stands and ground handling
Ramp crews work through the hottest part of the day in high-visibility clothing, and heat stress is measured as WBGT rather than air temperature.
- MaxiMet GMX552 WBGT heat stress with wind, T, H and P, 1.29 kg, IP66
- MaxiMet GMX500 wind, temperature, humidity and pressure for the apron
- MetConnect One where the stand needs third-party sensor inputs too
Hangar doors and maintenance areas
Large hangar doors carry a wind limit, and the interlock needs a measurement it can act on rather than a forecast.
- WindSonic 60 0 to 60 m/s, 0.5 kg, straightforward to mount on a door frame
- WindObserver 65 1, 2, 4, 5, 8 or 10 Hz output for faster interlocks
- Blade position sensors non-contact door and actuator position feedback
Fuel farm and hydrant system
Fuel storage is a certified hazardous area, so the wind sensor has to carry the certification before anything else about it matters.
- WindObserver IS ATEX, IECEx and UKEX certified, EN 60945:2002 for EMC
- LevelPro capacitive liquid level sensing with no moving parts
- LevelLite level measurement for smaller tanks and bowsers
Airfield construction and crane operations
Cranes working airside stop at a defined wind speed, and the reading has to hold up if the stoppage is ever questioned.
- WindSonic 75 0 to 75 m/s, full-range accuracy published
- WindObserver 90 0 to 90 m/s for exposed lifts
- MaxiMet GMX200 wind only, 0.5 kg, for a temporary works mast
UAV operations and airspace monitoring
Drone inspection and BVLOS work at an airfield runs to its own wind limits, on airframes where every gram counts.
- WindUltra compact 2-axis, IP69k, low power, built for mobile platforms
- WindSonic 60 0.5 kg ground reference for launch and recovery
- MaxiMet GMX200 portable wind reference for a temporary operating site
Environmental and air quality monitoring
Noise and emissions reporting is only as defensible as the meteorology recorded alongside it, and that record has to run for years.
- MetConnect THP WMO-compliant separation, two analogue inputs and a Pt100 input
- MaxiMet GMX551 wind, T, H, P, solar and rainfall in one compact station
- TruMet PW100 optical rainfall, 5 percent accuracy, no tipping bucket to clear
Ground support equipment condition
Tugs, loaders and steps fail on the stand rather than in the workshop, and oil tells you what is wearing before the failure does.
- WearDetect oil debris sensing for wear particles in lubricated equipment
- LevelLite fluid level in fuel, oil and hydraulic tanks
- Blade position sensors non-contact position feedback with no wearing parts
Calibration and verification
A reported wind speed is only defensible if it is traceable, and an accredited certificate is what closes the question.
- UKAS-accredited air velocity calibration traceable certification for anemometers and probes
- Multi-parameter calibration six parameters, equipment from any manufacturer
- Recalibration scheduling intervals, reminders and turnaround
Type and rate matter as much as temperature
Holdover tables are indexed by precipitation type and rate as well as by temperature. Freezing drizzle, snow and freezing rain behave differently on a treated wing, and the same air temperature produces different holdover times under each.
That makes the precipitation measurement the part most often under-specified. A gauge that reports accumulation over an hour is not describing a rate that changes within it, and a tipping mechanism that has frozen is not describing anything.
Humidity closes the set. The margin between air temperature and dew point decides whether moisture is depositing on the aircraft at all, and it moves through a night far faster than a forecast can track.
Everything then has to arrive together and continuously, because the decision is taken at the stand with an aircraft waiting and no opportunity to go and check an instrument.
Optical measurement has nothing to freeze
A tipping bucket depends on a mechanism moving freely, which is exactly what winter removes. Once it is blocked it reports a dry airfield during the event it was installed to measure.
TruMet PW100 uses infrared optical measurement rather than a tipping mechanism, measuring 0 to 200 mm/hr with 5 percent accuracy and 0.1 mm resolution. It outputs one pulse per 0.1 mm, replicating a tipping bucket, so it drops into a logger that already expects one.
Nothing to block, nothing to clear
View TruMet PW100A stopped anemometer reports calm
The failure mode that matters in winter is not an instrument that stops. It is an instrument that ices, seizes and keeps sending a number, because a calm reading is inside every limit and nobody questions it.
Ultrasonic measurement has no rotating sensing element to ice or seize. WindSonic M is heated aluminium operating to -40 degrees C, and WindObserver is heated 316 stainless at IP66, icing tested to MIL-STD-810F.
Heated, and honest about failing
Explore wind sensorsA de-icing decision is reviewed in the spring
Fluid consumption, movement rates and any winter occurrence all get reviewed once the season is over, and the review works from the conditions recorded at the time.
A conditions record with no calibration history behind it is an assertion. The same record from instruments on a traceable interval supports both the operational decisions taken and the fluid budget defended afterwards.
Labcal is an independent UKAS-accredited laboratory operating to ISO/IEC 17025:2017, calibrating equipment from any manufacturer, so temperature and humidity probes, pressure instruments and anemometers sit on one schedule.
What winter operations measure
Precipitation type and rate, temperature and humidity, and wind that keeps reporting through the weather it is describing.
Precipitation and conditions
TruMet PW100
Infrared optical rain gauge
The measurement holdover time is indexed against, made optically so there is no mechanism to freeze during the event.
MetConnect
Separable sensors for WMO-compliant siting
Temperature and humidity measured at the height they are comparable at, with third-party instruments brought into the same station.
MaxiMet
All-in-one weather station, no moving parts
One unit and one cable for a stand, a de-icing pad or a supplementary position that needs the full set of parameters.
Wind measurement
WindObserver
Heated 316 stainless open-head 2-axis anemometer
Heated 316 stainless for the positions that have to keep reporting through every hour of a winter the airfield operates in.
WindSonic
Lightweight 2-axis ultrasonic anemometer
WindSonic M in heated aluminium, operating to -40 degrees C, where weight and mounting simplicity decide where the measurement can go.
WindUltra
Compact 2-axis ultrasonic anemometer
Compact and low-power measurement for temporary positions and mobile equipment around the de-icing operation.
Where winter measurement does the work
Holdover at the point of application
Temperature, humidity and precipitation rate measured where the fluid is applied rather than across the field.
Remote de-icing
Conditions at the stand, where the decision is taken with the aircraft waiting.
Surface and approach
Precipitation rate feeding runway condition assessment and the decision to treat.
Consumption and budget
A conditions record that supports what was applied and why, when the season is reviewed.
Single position
One station carrying the winter parameters for a field that cannot justify several.
Crew and equipment
Conditions behind working limits for ramp crews and the equipment they operate.
UKAS-accredited calibration for six measurement parameters
Labcal is an independent UKAS-accredited calibration laboratory, Lab 0625, operating to ISO/IEC 17025:2017. It provides calibration across gas and air flow, air velocity, liquid flow, pressure, temperature and humidity.
For an airfield carrying thermometers, temperature and humidity probes, pressure instruments, anemometers and data loggers, a single accredited laboratory keeps the winter instrument estate on one traceable schedule.
Gas meters · Mass flow controllers · Dispensing systems
Anemometers · Pitot tubes · Thermal probes
Flow meters and sensors · Process control equipment
Gauges · Transducers · Manometers · Transmitters
Thermometers · Probes · Thermocouples · Data loggers
Hygrometers · Probes · Transmitters
Getting conditions to the stand and the pad
A holdover decision is taken at the aircraft, so the measurement has to arrive in front of the person taking it rather than in an archive.
Gill supports environmental monitoring, industrial sensing, embedded electronics and systems integration, so airport operators, handling agents and systems suppliers can bring winter measurement into operational displays and reporting.
Whether the requirement is a pulse output into an existing logger, Modbus into an operational system, or a serial string into a display, Gill engineers can support integration from specification through commissioning.
Outputs and options
- Modbus RTU : Site systems and SCADA
- SDI-12 & serial : Loggers and remote telemetry
- 4-20 mA & 0-10 V : Existing analogue channels
- Traceable calibration : So the record holds up on review
What the specification looks like in practice
Optical rainfall, nothing to freeze
Infrared optical measurement replaces the tipping mechanism that blocks in exactly the conditions holdover time is calculated for.
A pulse output that drops in
One pulse per 0.1 mm replicates a tipping bucket, so an existing logger does not need rewriting.
Heated across the range
WindSonic M operates to -40 degrees C in heated aluminium, and WindObserver is heated 316 stainless, icing tested to MIL-STD-810F.
No rotating element to seize
The failure that matters is an iced anemometer reporting calm, and ultrasonic measurement removes it.
Sited where the decision is taken
Compact stations put the measurement at the pad or the stand rather than at a reference position across the field.
Evidence when the season is reviewed
Independent UKAS-accredited calibration across six parameters, for equipment from any manufacturer.
Questions about de-icing and winter operations
Temperature, humidity and the type and rate of precipitation falling at the time. The holdover tables are indexed against those, and the same air temperature produces different holdover times under different precipitation types.
Because it depends on a mechanism moving freely, and winter is what stops it. A blocked gauge reports a dry airfield during the event it was installed to measure.
TruMet PW100 uses infrared optical sensing with no moving mechanism, measuring 0 to 200 mm/hr with 5 percent accuracy and 0.1 mm resolution.
On an airfield that operates through freezing conditions, yes. WindSonic M is heated aluminium operating to -40 degrees C, and WindObserver is heated 316 stainless at IP66, icing tested to MIL-STD-810F.
As close as practical to where the decision is taken. Conditions at a de-icing pad or a stand can differ from a reference position across the field, and the holdover decision is taken at the aircraft.
Generally yes. The sensors provide serial, Modbus, analogue and pulse outputs, and the engineering team can advise on the interface a particular operational or reporting system expects.
Yes. Labcal is an independent UKAS-accredited calibration laboratory, Lab 0625, operating to ISO/IEC 17025:2017, calibrating equipment from any manufacturer across gas and air flow, air velocity, liquid flow, pressure, temperature and humidity.
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