The Crosswind myth at Argyle!

by Mike Arthur

First, allow me to introduce myself. I retired as a professional pilot recently, but continue to fly privately. I have over 21,000 hours on aircraft ranging from single engine propeller to heavy multi-engine jet (Boeing 747). I have extensive airline and corporate jet experience operating throughout the World, including seven years in the Caribbean. I feel qualified to comment on the largely erroneous statements that have appeared in the media with regard to the operational aspects of the Argyle International Airport.{{more}}

I cannot and will not comment on the eventual opening date, but the new airport is going to be finished and will be capable of safely handling aircraft flown by competent pilots. There are almost no airports in the world that do not have some “issues” that can have an influence on safety. ICAO (International Civil Aviation Organization) lays out in Annex 14 – “Aerodrome Design and Operations” all the requirements that should be met when planning an airport. If, for some reason, i.e. terrain, the requirement cannot be fully achieved, the airport can still be built. Variations to Annex 14 can be allowed, but may result in some restrictions on operations. I am not privy to the details of Argyle, but having been to the site and operated into hundreds of airports, I can see no reason for any concern.

Let me now address the topic that has been the subject of considerable misinformation, if not downright lies. Argyle is situated on the coast close to sea level (less than 100 feet elevation?). It would be logical then to assume that the wind in the vicinity of the coast would be very similar to that experienced at the airport. Ask anyone who has sailed the islands and they will tell you that this area is affected by the “North-East Trades”. If this opinion is in doubt, a search of the Internet will confirm this to be true with records going back hundreds of years. Most people who live here tend to think that the wind is from the east. Not true! The majority of the time the wind is from a point well north of due east, and certainly not, as has been suggested recently, from the southeast. The wind can, and does blow from all points of the compass, BUT, the prevailing wind is from the north-east. Usually 060 to 070 degrees true, at 10 to 20 kts. Any sailor will tell you that it is much easier to sail from St Lucia to St Vincent than the reverse. Could be something to do with the prevailing wind – do you think!

Ok, I hope that most of you will now accept where the wind is really coming from and the effect it will have at Argyle for a very large percentage of the time.

I would now like to address the position and orientation of the runway. Startling fact – St Vincent is a beautiful, but hilly and mountainous country. Finding an area that is relatively flat is a challenge. To find that same area that is orientated into the prevailing wind is well nigh impossible. The planners of Argyle have done an excellent job of compromise. Anyone with a computer can pull up a very good satellite photograph of Argyle dated 2015. It shows clearly the partly finished runway. Google maps are displayed with TRUE north at the top. It is therefore very easy to measure the true runway bearing. I made it very close to 021 degrees (true). I then looked up the magnetic variation, which for St Vincent is 015 degrees west. That makes the runway 036 degrees magnetic. I would expect that the runway will be designated 04/22. Why is it so important to use a magnetic bearing? Simple, that is the value that is displayed on the compass in every aircraft. An aircraft heading is always a magnetic heading. The wind direction reported and passed to aircraft is always magnetic. That is for the windward side of St Vincent it is usually 075 to 095 degrees magnetic. Even for those who are mathematically challenged, it is very plain that the airport will not, under normal wind conditions, be subject to a wind at 90 degrees to the approach.

Some “experts” have quoted from ICAO Annex 14 – Aerodrome Design and Standards – suggesting that Argyle will not conform to the cross-wind limits. This document gives guidelines when planning an aerodrome. They have not read the document carefully and in at least one case quoted from an FAA document. ICAO suggests that the runway orientation should be such that 95 per cent of the time the cross-wind component will not exceed the value (in Annex 14, 3.1.2) for the most “critical” aircraft expected to use the aerodrome. (Note – critical in this context is the largest aircraft.) In the case of Argyle, that number is 20 knots (with good braking action). This is just one component of the layout planning. In the case where multiple runways are planned, this parameter is used to establish runway directions. It is not a limitation. When certifying an aerodrome the Authority will use Annex 14 to ensure that the guidelines contained within that document are addressed. If there are any areas that cannot be complied with, it is possible to request under Appendix 3 an “Approval of Deviations”. If approved, it is necessary to ensure that, for example, pilots using the airport are aware of the deviations. Since it is unusual for the wind to exceed 20kts, it seems unlikely that any “deviation” for wind will need to be addressed.

No aircraft manufacturer lays down the maximum permissible crosswind for their products. They only list the “Maximum Demonstrated Crosswind” achieved during certification testing. It is up to each operator to lay down in the company “Operations Manual” the “Maximum Permitted Crosswind Limit”. In the case of large aircraft such as Boeing 767 or 757, this is usually around 30 knots. The obvious question is why if ICAO were to lay down a crosswind limit of 20 knots, would manufacturers build aircraft that can safely exceed this number at least 50 per cent? ICAO Annex 14 is for planning an aerodrome, not for certifying that aerodrome.

Remarks have been made that because there is a vertical cliff face at the southern approach end, it will generate turbulence, endangering aircraft. How the writer would know this, I have no idea. If he has proof, with supporting test data, perhaps he would like to share it with everyone. In the original planning document, the threshold (the start of the runway landing area) was to be displaced. For reasons that are not immediately apparent, this is no longer the case. It must be pointed out that there will be a lighting system to show the ideal approach path (day and night). Following this indicator will bring an aircraft over the threshold at 50 feet for a touchdown 1000 feet down the runway. This is Standard Operating Procedure (SOP) and is taken into account for all aircraft during certification. If pilots follow this SOP, there is no reason why they should encounter flight hazardous turbulence. We will see!

So, in conclusion, what will we have soon in St Vincent? A new airport that is operational, superior in every way to ET Joshua. A longer, wider runway, with no terrain obstructions. Is the orientation perfect? No. I would, however, consider it safe for commercial or private aircraft flown by competent pilots. This is based on my years of real experience flying a wide variety of aircraft into hundreds of different airfields in every conceivable weather situation.

I have restricted my comments to the areas in which I have extensive experience. I would also suggest that persons refrain from speculation, unless they are qualified and have irrefutable proof that there really is a problem.