Ownership of risk

[Aurora Australis]

I do not understand the reference to flying with regard to TAFs or indeed METARS. Unless things have changed out of all recognition, wind forecasts and observations are with respect to anemometer height. Flying at 30 feet through the area at 30 ft. sounds intrinsically dangerous.

The point I think BV is making is that the TAFs do include a forecast of conditions above anemometer height - the part of the TAF that appears to trigger the closure of the airspace is the 56//// turbulence code, typically for turbulence up to 3000'. The rest of the TAF often does not contain anything suggesting conditions that would cause major concern. Until recently, it was just the runway that was closed - aircraft could still transit the zone during the forecast conditions, and regularly did (without falling out of the sky or losing control......).
As BV said, you would expect the METARs to bear some similarity to the conditions forecast in the TAF, yet frequently (e.g. as per the data copied in my post #54) there is very little correlation. The accuracy of the TAFs is presumably assessed for quality control - (I would be interested to see the Met Offices own assessment of how accurate the MPA TAFs are), but how is the accuracy of the turbulence forecast for the layers above the airfield assessed, without allowing aircraft through?
A subjective assessment by the majority of pilots I know who have used this airspace over the past 30 years is that recently, the TAFs often seem extremely pessimistic, and the actuals often bear no resemblance to the forecast.

Once again, at the risk of labouring the point, none of us locally think that inbound aircraft should land regardless of conditions, but just that there should be some flexibility, particularly when the forecast conditions are nowhere near materialising.
Yesterday, the forecast was for severe turbulence, and I have no doubt it did occur, and would not have been a day to mess with - but the actuals were reflecting this, e.g. 340/30g46, and 320/09 tempo 350/20g30. (The southbound airbridge was delayed 24 hours).

[Aurora Australis]

Like I have alluded to, whatever you think of the Met’s output or whether the Airfield Operator is being overly zealous with the restrictions during forecasted rotors it is irrelevant. Ultimately, if you are not happy with the situation and want to own the risk yourselves, get your own airfield!

CBTL - Mount Pleasant Airfield does not belong to the RAF. It was built, at UK taxpayer expense, to allow for defence of the islands from a belligerent and bullying neighbour, but also to act as the International airport for the Falklands, to allow it to develop economically.

The question remains why the Operator is assessing the risk in a way that seems to be unique, when it appears that there are airports with similar or worse wind/turbulence issues that are not closed in the same way.

Your solution of building another airport would lead to one already under-utilised expensive asset being supplemented by an even more under-utilised one!

[Bing]

Originally Posted by Could be the last?

BV - AA,

Like I have alluded to, whatever you think of the Met’s output or whether the Airfield Operator is being overly zealous with the restrictions during forecasted rotors it is irrelevant. Ultimately, if you are not happy with the situation and want to own the risk yourselves, get your own airfield!

The airfield operator doesn't own any risk, see RA1020, they are responsible for providing a safe operating environment and that should include informing users of any potential adverse weather. The risk owners are the DDHs for the military platforms that operate there and the accountable managers for the civilians who, having been made aware of the rotors issue in the airfield hazard log, then make their own assessment on the risk reduction activities.

[Could be the last?]

Bing,

Correct, however, I didn’t say that the Airfield Operator owns the risk. But, I would argue that he or she would be in a whole world of pain when something goes wrong post a rotors forecast!

[langleybaston]

Originally Posted by Aurora Australis

The point I think BV is making is that the TAFs do include a forecast of conditions above anemometer height - the part of the TAF that appears to trigger the closure of the airspace is the 56//// turbulence code, typically for turbulence up to 3000'. The rest of the TAF often does not contain anything suggesting conditions that would cause major concern. Until recently, it was just the runway that was closed - aircraft could still transit the zone during the forecast conditions, and regularly did (without falling out of the sky or losing control......).
As BV said, you would expect the METARs to bear some similarity to the conditions forecast in the TAF, yet frequently (e.g. as per the data copied in my post #54) there is very little correlation. The accuracy of the TAFs is presumably assessed for quality control - (I would be interested to see the Met Offices own assessment of how accurate the MPA TAFs are), but how is the accuracy of the turbulence forecast for the layers above the airfield assessed, without allowing aircraft through?
A subjective assessment by the majority of pilots I know who have used this airspace over the past 30 years is that recently, the TAFs often seem extremely pessimistic, and the actuals often bear no resemblance to the forecast.

Once again, at the risk of labouring the point, none of us locally think that inbound aircraft should land regardless of conditions, but just that there should be some flexibility, particularly when the forecast conditions are nowhere near materialising.
Yesterday, the forecast was for severe turbulence, and I have no doubt it did occur, and would not have been a day to mess with - but the actuals were reflecting this, e.g. 340/30g46, and 320/09 tempo 350/20g30. (The southbound airbridge was delayed 24 hours).

Thank you. I must make the point that I retired as a Chief Met Officer in the UK Met Office in 1996 and had never heard of a 56//// group. I would have been startled to be asked to predict quantitatively in a TAF something that could not be measured Everything else in a TAF can be checked against the actual [not necessarily a METAR, but certainly a SYNOP.] The non-critical exception is cloud base above the effective range of the relevant devices. Perhaps memory fails me.
I have searched Google but cannot find chapter and verse for the 56 group coding.
It is well understood that turbulence, other than convective, is a mysterious beast. Our investigations into CAT using aircraft reports and aircraft chasers demonstrated that it is like a shoal of fish in the ocean .......... mobile, transient and fickle. This included CAT nearer the surface than jet streams, but we only came up with generalisations such as coastlines, mountain ridges etc. Rotors and lee waves were acknowledged as very very difficult to predict, especially in dry air with no tell-tale cloud. Our numerical models became so good at jet levels that, as a by-product, CAT at these heights became better understood and better forecast, but far from perfect.
I am left wondering what has changed in 20 years regarding low-level terrain-induced shears and turbulence. Understanding? I doubt it. Measuring? I doubt it. Predicting? I doubt it.

[Aurora Australis]

Langleybaston - thanks for that interesting bit of background info on turbulence.
You said

I have searched Google but cannot find chapter and verse for the 56 group coding.

I suspect from your background that you may be looking for something more technical (i.e. how the model for generating the forecast turbulence works), but in case you are just looking for the meanings of the codes, this is from the "US Air Force Aircrew Quick Reference to the TAF and METAR codes"

"If forecasted, the turbulence code will be prefixed by the number 5, and will follow the cloud or icing group. To decode, follow these instructions: 1. Look for the turbulence designator “5” that follows the cloud or icing group (520004).
2. The next digit will determine the intensity (520004). See Figure 4.
3. The next three digits will determine the base limit of the turbulence layer in hundreds of feet AGL (520004).
4. The last digit will determine the turbulence layer depth in thousands of feet (520004), so add this value to the base height to determine the top limit of the turbulence conditions.
In the above example, the turbulence forecast will read, “occasional moderate turbulence in clear air from the surface to 4,000 feet.”

Figure 4. Turbulence Intensity Decode Table
0 - None
1 - Light turbulence
2 - Moderate turbulence in clear air, occasional
3 - Moderate turbulence in clear air, frequent
4 - Moderate turbulence in cloud, occasional
5 - Moderate turbulence in cloud, frequent
6 - Severe turbulence in clear air, occasional
7 - Severe turbulence in clear air, frequent
8 - Severe turbulence in cloud, occasional
9 - Severe turbulence in cloud, frequent
X - Extreme turbulence
Note: Occasional is defined as occurring less than 1/3 of the time"

You also said you wondered what had changed in 20 years regarding low-level terrain-induced turbulence. I can only assume that they have developed some new modelling of what they think happens - I am just not convinced from experience and observation that they yet have a model that is "fit for purpose"!

[Aurora Australis]

The airfield operator doesn't own any risk, see RA1020, they are responsible for providing a safe operating environment and that should include informing users of any potential adverse weather. The risk owners are the DDHs for the military platforms that operate there and the accountable managers for the civilians who, having been made aware of the rotors issue in the airfield hazard log, then make their own assessment on the risk reduction activities.

Bing - thanks for that. That is how I would have thought it should work. So maybe I am using the wrong terminology when I titled this thread "Ownership of risk". I thought that was what had changed, to make the Airfield Operator so risk averse.
So if as you say above, the accountable manager for the civilian operators should make their own assessment of the risk reduction activities, why is it that when LATAM (LanChile), FIGAS (Falkland islands Government Air Service), HiFly (the oil charter flights back in 2015/16), the Air ambulance flights from Chile, are all willing to make their own decisions on whether the conditions are acceptable, they are still over-ruled by the Airfield Operator?

[Bing]

Originally Posted by Could be the last?

Bing,

Correct, however, I didn’t say that the Airfield Operator owns the risk. But, I would argue that he or she would be in a whole world of pain when something goes wrong post a rotors forecast!

Not if he's taken the necessary measures to inform the operators, the risk and blame would be entirely on them. Now if there were actual rotors the AO should close the airfield as it's not a safe operating environment, but with the forecasting of them being so unreliable it could be argued they're creating extra risk by forcing aircraft to return to the mainland when they're only twenty minutes from the islands.

[langleybaston]

AA.
Thank you very much, that is what I was looking for.
Damned if I know how I would go about quantifying it.
Clever people these days.

[Could be the last?]

Bing,

My understanding is that there are the necessary procedures in place wrt how crews/DDHs are informed of rotors. However, consider the unique status that MPC has (discussed previously) if the main was blacked what is the mitigation? Furthermore, if, as you say the forecast is unreliable, then the option to turn an ac around/divert could be argued as the safest option 'knowns v unknowns' however much it is a pain in the backside to go elsewhere.

[Aurora Australis]

To show the scale of this problem at MPA, and the impact it has on the islands -

Looking back over the TAF records between 01 Nov and 15 Dec, (and using the current policy rules that changed in mid Nov to include +/- 1 hour either side of forecast turbulence), during a period of 1080 hours, the airfield would have been closed to all fixed-wing traffic for 263 hours, a closure rate of 24.3%.

Is there any other international airport that is closed due wx anything close to this amount? This policy seems unique, and I am sure that the turbulence issues at MPA are not unique.

[renard]

Isn’t St Helena closed about 100% of the time....

[Aurora Australis]

Interesting question renard. While it clearly is not closed 100% of the time, it is affected by turbulence. Does anyone here know whether St Helena airport gets closed by NOTAM, i.e. prohibited by the airfield operator, or whether it is the aircraft operators who make the decision whether to fly depending on their limits as per their ops manuals?