Holdover time expired in freezing fog and light snow
You are the commander of a turboprop departing a northern European airport at night. The temperature is -2 degrees C with freezing fog and light snow, wind 040/4 kt. Runway 04 is in use but the parallel runway is closed because of a disabled aircraft, so departure traffic is queuing. Your aircraft is de-iced and anti-iced with a Type I fluid, and the ground crew's record shows the final application started at 22:41, giving a holdover time of 20 minutes under the operator's tables. You taxi at 22:44 and are number seven in the queue. At 23:03 you reach the holding point; light snow is still falling and there is no sign of it stopping. The first officer says you have only just gone over, that the wings look shiny but they always do, and the cabin crew reports no frost inside. Your take-off performance was computed for a contaminated runway and is legal.
1. When does the holdover time start, what does it apply to, and what is the status of this aircraft at 23:03?
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The holdover time starts at the beginning of the final application of the anti-icing fluid - not at the start of the de-icing step and not when the aircraft leaves the pad. The record shows 22:41 for final application, so at 23:03 twenty-two minutes have elapsed against a 20-minute holdover time for Type I fluid in freezing fog and light snow.
Two things follow. The holdover time has expired. And it is a guideline, not a guarantee: the tables are built around defined precipitation intensities and temperatures, and freezing fog with light snow near the lower end of Type I performance is exactly where fluid failure can occur earlier than the table suggests.
The legal obligation is the clean aircraft concept. The operator must have procedures for de-icing and anti-icing, and the commander must be satisfied before take-off that the critical surfaces - wings, tail, flight controls, engine intakes and the surfaces visible from the flight deck - are free of contamination. Ice, snow, frost or a refrozen film changes lift and drag in ways the performance figures were not computed for. 'Only two minutes over' is not an argument; the holdover time is not a soft limit that a crew may round.
2. What do you do at the holding point? Work through the options, including any inspection or check that might let you take off.
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You do not take off. At 23:03 the holdover time has gone and snow is still falling, so the only defensible options are a new application of fluid or no flight.
Option 1, a pre-take-off contamination check. This is a defined procedure, not a look out of the window. It is permitted only where the operator's approved procedures allow it, with the specified inspection method and in conditions in which contamination can actually be detected, and it cannot be used in active snow to manufacture more holdover time. If the operator's procedures do not authorise it for this type and these conditions, it is not available. The first officer's 'the wings look shiny but they always do' is not a check.
Option 2, a tactile check. Some operators permit one where the critical surfaces can be reached safely, but it is a contamination check, not an extension of holdover time, and it does not override an expired table in falling snow.
Option 3, return for another de-icing and anti-icing application with a new fluid record and a fresh holdover time, then depart provided the runway can be reached inside it. That is the realistic answer, and it needs ATC coordination: tell ground or tower you are returning for de-icing and ask to be kept in sequence for the runway after the new application, not sent to the back of another 30-minute queue. If the queue cannot be managed, hold at the stand until the weather or the flow improves, or delay the flight.
Throughout, keep the cabin informed, recompute performance for the actual conditions, and remember that the clean-aircraft decision belongs to the commander, not to the dispatcher and not to the slot.
3. The de-icing provider says its 20-minute figure is conservative and offers to sign the record. Does that change anything?
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No. The provider's opinion does not turn an expired holdover time into a valid one, and the signature on the de-icing record documents what was applied and when; it does not certify that the aircraft is clean at the holding point. The commander has to be satisfied about the state of the aircraft, and the way to be satisfied is a new application with a new timer.
It is worth separating two things the provider may be mixing up. The holdover time table is a planning aid based on standard test methods for the fluid. The provider may genuinely believe local experience is better than the table; if the operator believes local conditions justify a different procedure, that is a change to the operator's ground de-icing and anti-icing procedures, approved through its management system and its authority and supported by the fluid manufacturer's data - not a decision taken by a provider at the pad and accepted by a crew that wants to go.
The same applies to any suggestion that the snow is light enough to ignore. Precipitation intensity is part of the conditions on which the published holdover time depends; snowing harder than the table assumes makes the time shorter, not longer.
Decision: return for a further application, record fluid type, concentration and time, obtain a new holdover time, and if the delay cannot be contained within it, do not depart. File a note for the operator's safety management system: a 22-minute taxi in these conditions is a procedure problem, not a one-off.