Wednesday, January 30, 2019

St. Helena Airport Tour

By Jack

On January 19, Josh and I spent the afternoon at the St. Helena Airport/FHSH getting a "behind the scene" tour of the met office and the control tower. Many thanks to meteorologist Tim Baker and ATC specialist Bernard Msengeti for hosting us to this most unique operation.

Tim and Bernard have a great view from their "offices"...

The Met Office

We started in the met office with Tim explaining his work and schedule. The St. Helena met office is operated by the UK Met Office and Tim works for the UK government. There are a handful of remote  meteorological offices run by the main UK Met Office and UK based meteorologists "bid" on temporary assignments (generally six months at a time) at those exotic locales...St. Helena, Gibraltar, the Falkland Islands, and Rothera Base in Antarctica to name a few. Tim has served in Gibraltar and St. Helena on two tours.

As mentioned in a prior post, the forecast the St. Helena Met Office produces goes way beyond the typical terminal area forecast (TAF) we receive at home. A normal TAF is produced for St. Helena, but there are also regular three day outlooks and specific detailed forecasts for each day a flight is scheduled to arrive.

A sample three day outlook...

The detailed forecast for our arrival date...

And the normal TAF for our arrival date which does not seem very useful in comparison to the other two forecasts...

Tim gave us a very detailed telephone briefing the day before our flight and explained that due to the topography around the airport, there often can be low clouds over the center of the airfield yet the approach ends of each runway can be mostly clear. Thus, there are occasions when the formal report of the cloud base taken at mid-field shows low cloud, but arriving aircraft can clearly see the landing zone at the end of each runway. This can create an unusual situation where arriving pilots report the runway in sight yet the plane cannot be seen from the control tower or the met office.

Another very unique feature of the St. Helena met operation is the use of LIDAR (Light Detection & Ranging) to evaluate the wind conditions on the approach path to the runway. LIDAR is a form of radar that uses a laser pulse rather than radio waves to survey the atmosphere. For the St. Helena airport, the LIDAR is located at the end of the runway and focused up at an angle of three degrees along the normal approach path. Using the LIDAR equipment, the wind speed to or from the LIDAR unit can be displayed at a continuous range from the end of the runway out several miles.  Wind shear is, in effect, a rapid change in wind speed or direction over a short distance. Using the LIDAR some types of wind shear can be detected directly.

For example, in the image above one can see a rapid change in the relative wind velocity off the approach end of runway 20 (LIDAR pointing north - azimuth 359 degrees true) at about 11:40 UTC from a positive 5 m/s at about 400 meters from the end of the runway to a relative velocity of about negative 5 m/s around 600 meters from the runway.

When we landed on January 17, I reported to Tim that we had experienced some light wind shear on short final. He said he had expected as much from the LIDAR display. Pretty neat. Using LIDAR for wind shear detection is not a common technology and is employed at only a few airports around the world (the Hong Kong airport being one).

The Control Tower

After the very interesting met office briefing, we went upstairs to the control tower "cab."  The twice weekly SA Airlink flight was due to arrive in about an hour and we were invited to observe its arrival from the tower. This turned out to be more exciting than expected.

ATC specialist Bernard Msengeti gave us a tour of the tower and the equipment they use which is mainly fairly typical for a air traffic control tower. Displays of wind (center and each runway end), clouds, visibility, VHF radios, an HF radio (rarely used we were told), and telephone links to Luanada Oceanic which controls all flights until they are "handed-off" to the St. Helena tower.

The view from the tower is impressive...

As the Airlink flight approached the airport, the clouds were not clearing as rapidly as expected.  The flight crew asked for the same RNAV DME LOC Rwy 20 we had used two days prior and Bernard cleared them for that approach.

As time passed and we knew the Embraer 190 aircraft should be close to the runway, but we could not see anything but broken clouds. Then we suddenly saw the plane break out of the clouds about 400 FT above the runway, but well to the left of the normal approach path.  We saw the plane start to turn right in order to align better with the runway, but it almost immediately executed a missed approach and disappeared back into the clouds. Tension in the tower increased as the crew reported the missed approach and said they were circling around for another try using a visual approach.

The go around looked wise to us given their low altitude and being so far to the left of the runway centerline. Attempting to salvage the approach probably would have been difficult and unstabilized.  We aren't sure why they were so far off course, but guess they were attempting to maneuver visually in order to keep the runway in sight through the broken clouds and just could not maintain visual contact along the extended runway centerline.

As they circled around for a second attempt, we could not see them at all. Clouds were pretty solid over the center of the airfield and the control tower. However, as mentioned above, due to the unusual topography around the airport, it is not uncommon for visibility from the tower to be more restricted than what pilots can see on the approach path.

So we all waited in the tower to see how this approach would work out.

After a few minutes, we saw the plane on final approach at about 500 FT above the runway and well aligned. We can't be certain, but from our perspective it looked like the crew would not have seen the runway until on short final. This time the plane got over the runway normally, but "floated" down the runway just a few feet off the pavement without touching down. At about the halfway point on the runway and with the wheels still not down on the pavement,  the crew executed another go around. At this point the tower was quiet and you could cut the tension with a knife. No one knew if the plane had enough fuel for a third attempt or would need to divert to Ascension Island over 700 NM to the north.

Once again the go around looked like a wise move to us. With less than half the runway remaining to get down and stopped, it was just too risky to continue the landing attempt. This is especially true at St. Helena given this note in the pilot briefing information about the airport...

At some airports in the unfortunate event that an aircraft runs off the end of the runway, there is a nice extended area of relatively level ground on which to stop.  The plane may be damaged, but everyone is likely to walk away. At St. Helena there is a 1,000 FT shear cliff to the ocean very close to the end of the runway.

Smart move by the AirLink crew to go around given the risks of not getting stopped in time.

Everyone in the tower was waiting to hear if they were diverting to Ascension Island or going to make another attempt. After a couple of minutes the crew called and requested the RNAV DME LOC Rwy 20 approach again (not the visual). We all assumed this would be their last attempt before a diversion would be required.  Fortunately, this third approach attempt worked out well with a perfectly normal landing. Everyone in the tower breathed a little more easily. We knew the passengers on the plane were likely pretty shaken-up and later heard several came off the plane in tears. But, they were there safe and, from our perspective as pilots, the AirLink crew had made the right decisions with the two missed approaches.

The FlightRadar24 track of the January 19 flight...

Having had enough excitement for the day, we bid Tim and Bernard goodbye and headed back into town. The next night we hosted Tim and Bernard's ATC colleague Bramwell to dinner in town which was a lot of fun (Bernard was invited but not available for this last minute get-together).

The next day (January 20), we had to depart St. Helena and start our four day "sprint" back home to Austin.  We wished we had had more time in St. Helena as it was most fascinating and friendly place.

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