Hold Over times

[Tom4]

Hi guys, short and simple question.

Regarding the hold over times, usually hold over time after deicing/anticing is "always" some between, for example 0:25 - 0:40 .

Do you have any procedure in your company which time you choose? 25minutes or 40minutes?

[HOVIS]

Is this a serious question?

[Tom4]

Yes, really. I would really appreciate any serious quidance

[HOVIS]

You don't 'choose' the holdover time. It is dependent on ambient conditions, precipitation, temperature, fluid type and concentration.
Each application is unique.
I have no idea where you have got your figures from.

[Tom4]

Yes I agree.

But my question is, this time depends on actual weather conditions, and etc....then we will get actual hold over time, which is usualy some time between some defineted period of time, for example, from 20min to 55 min . but which one it is?

[Qwark]

The time range is to allow for precipitation intensity. The higher time refers to “light” precipitation and lower time refers to “moderate” intensity. In principle “heavy” precipitation does not permit a take off however there is some exceptions and associate procedures these days!

[Tom4]

Thank you for asnwer.

But if you have in the table already specified "light snow" or "moderate snow", what then?

Or if you chose table according to prevailing function of visibility?

[Capt Scribble]

The deicing should do 25 and might do 40 depending on intensity of precipitation. A visual check of the wings might be an idea over 25 mins.

[Max Angle]

It basically comes down to the commanders assessment of the conditions and their judgement on the state of wing, it is one of the things you get paid more money for. Been back for a look quite a times over the years, much the bemusement and amusement of the pax, who you need to turf out of their seats to get near the window.

[ScepticalOptomist]

Thank you for asnwer.

But if you have in the table already specified "light snow" or "moderate snow", what then?

Or if you chose table according to prevailing function of visibility?

The higher value of HOT is for light snow. The lower value for anything greater than light snow up to moderate. If outside your window you assess the intensity as worse than moderate, you don’t go.

[Qwark]

Much of the HOT information I have read about this topic originates from Transport Canada and FAA winter operations guidelines. I think it’s important to remember this is all to assist the judgement of the Captain. HOT is not a limitation, just a guide. Based on elapsed time and conditions a take-off may be permitted following an inspection. There are different types of inspections!

I would suggest some time searching FAA and TC websites with some background information regarding HOT tables if your Airlines doesn’t provide it. The tables alone are only a small part of the story!

[SITTINGBULL]

This online course by NASA is pretty good in regards to general De-Ice / Anti-Ice ops.

https://aircrafticing.grc.nasa.gov/

[smacjet]

Hi guys, short and simple question.

Regarding the hold over times, usually hold over time after deicing/anticing is "always" some between, for example 0:25 - 0:40 .

Do you have any procedure in your company which time you choose? 25minutes or 40minutes?

My favorite miss-understood topic in aviation!

This is really easy, once you get started on the 'right path'.

1) The range in a table IS NOT min and max times!
-Probably the most confused topic in aviation. These times are representive of 'rate of precipitation'.
Very light snow has a liquid equivalent snowfall rate of 0.3 to 0.4 millimeters per hour (mm/h), and light snow has a rate of 0.4 to 1.0 mm/h. (For reference, moderate snow has a liquid equivalent rate of 1.0 to 2.5 mm/h, and heavy snow is greater than 2.5 mm/h.) The longer times for very light snow would correspond to the lesser rate, whereas the shorter times would correspond to higher rates.

2) For example lets have a METAR that has -SN with 1 1/2 sm visability (night, -4 &100%)...
-The 'type' which is refered to as 'precipitation intensity' is SN, but...which one? (We don't ever use the '-' in front of the SN...Its not light snow (-SN), no,no,no!)

How to figure what 'precipitation intensity' of snow? Snowfall Intensities as a Function of Prevailing Visibility table.
In that table, we are directed to pick a color coded box...In our example, we now have Moderate Snow (orange box).

3) Next, we go to a Type IV generic holdover table...using the conditions I randomly picked:
-Moderate snow (orange box again) is represented in the table as 0:30-0:55 minutes. From the weather scientists, moderate snow is equal to 1.0 to 2.5 mm/h.
Next, go outside on your factory installed snowfall accumulation guage. If its 1.0mm/h use 55 minutes! (2.5 millimeter per hour is only 30 mins). Done!

Don't have the 'factory installed snowfall accumulation guage' option? Hum...we know that we have Moderate Snow, however, we don't know which one.
I'll let you be the judge as to what is the best option to pick (Transport CA guidance is that the lowest number must be used, think the FAA is getting onboard that too in the 22-23 guidelines).

4) Procedure time (from my department, written by me, plagiarized from many...

Holdover time is good for 0:30 minutes (most restrictive).
Fluid under most optimal 'Moderate Snow' conditions good for 0:55.
We 'hold' for 30 minutes, beyond 30 minutes we 'must' do a Before Takeoff Critical Surface Inspection...(Ours is a visual check within 5 mins of Take-off to verify the fluid is still effective).
Beyond 55 minutes, a tactile check must be done (by the experts, not the pilots)...however, if good, this would require zero continuing precipitation and takeoff in 5 mins to go fly.

Hope this helps! It is a really good question. Also, thanks for asking it, that says a lot about you as a pilot. I hope I get the 'lucky draw' to ride in the back on one of your flights. As I do many positioning activites in my flying, I am very aware of the trust that others place in us. Stay safe!

[RocknRola87]

Have a look on FAA N 8900 series notice, it will help you understand what does it mean the span time for each precipitation case. Personally we don’t have specific company guidance on that matter.

[avionimc]

As sitting bull said:
https://aircrafticing.grc.nasa.gov/2_3_3_1.html
Which Fluid is Right? Fluid Basics

check also FAA AC 135-17