Trying to land in freezing fog

The weather today was pretty grim, the forecast was for low cloud and fog all day and you just know its going tone one of those days when you aren’t going to get home.  I packed some extra stuff in my bag before I left in case I ended up night stopping, which with the way the weather was heading, was looking increasingly likely.

The forecast in Birmingham was for broken clouds at 200ft and overcast at 300ft, this means that you pretty much aren’t going to see anything at 300ft and you may be able to see something at 200ft.  The clouds are reported above the aerodrome level.

For landing at Birmingham using the category 1 ILS we must make a decision at 510ft, this is above sea level and Birmingham has an altitude of 305ft, this means that we are between the broken and the overcast clouds and therefore unlikely to see the runway before we have to abandon the approach and go-around.  Additionally there was mist forecast on the runway with a visibility of only 600m which meant we could make an approach into Birmingham but that we would probably have to initiate a go-around.  To make matters worse, because of the freezing fog we would be landing in icing conditions which meant the aircraft would have to fly faster and be a much more difficult thing to get on the ground.

We decided before we departed that we would be using Manchester as our alternate, that is, we would make one attempt into Birmingham and then turn around and head to Manchester instead where the weather was better. 

I have flown quite a few flights down to minima before and it makes me quite nervous, there is something about watching the altimeter reading lower and lower numbers until it is not much higher than your house before you decide whether to land or go-around, and the chances are that you won’t have seen anything when it happens.  I have put this down to watching all of the air crash investigations where some form of human error has taken place and the aircraft has ploughed into the side of a mountain or hit the ground 1 mile short of the runway, these are called CFIT, or Controlled Flight Into Terrain.  This is where there is no problem with the aircraft and similarly, the crew are unaware of any danger, the aircraft is simply flown in a controlled manner, into the ground.

There are different categories of landing systems available, the Dash8 can fly using categories 1 & 2, there is then categories 3, 3b and 3c.  Category 1 is usually deciding around 200ft above the ground on the barometric altimeter, it’s therefore vitally important to have the pressure set correctly and to verify distance and altitude against the approach plate.  Category 2 is usually deciding at 100ft above ground on the radio altimeter which is a much more accurate piece of equipment to measure height, it also requires extra procedures, training, and currency (certain number of landings in a set period).  Category 3 goes right down to having the aircraft automatically land onto the runway by itself, in up to zero visibility. For auto land to be allowed the aircraft must have independent autopilot systems and an auto throttle, the Dash8 has neither of these and hence it can only land to category 2 limits.

The captain on my flight was out of currency and hence we could only land to category 1 today.  The captain was going to be making the landing and I did feel for the captain slightly because the conditions were far from ideal and the ILS at Birmingham seems to have a slight bend in it positioning you slightly off to one side at around the moment you want to decide to land or go around for category 1.  As we started our final descent into Birmingham it was actually a really nice clear evening, it was only when we became established onto the ILS at 3000ft that we could see the fog and the mist below us.  We continued descending and were handed over to Birmingham tower who informed us that the rvr and the cloud based were still 600m and 200ft, the captains finger was covering the go-around trigger more than usual, the trigger would start the chain of events that would have us leaving the runway below us like a scalded cat.

As we descended throu 1500ft the cloud and mist started to drift across the aircraft and then when we descended through 1000ft, suddenly everything was gone and all we had was the white cloud in front of us lit up by the landing lights and the intense bright flash of the white strobes on the aircraft. We were cleared to land and my heart started to beat a little bit faster, we reached our first checkpoint as the radio altimeter called out ‘five hundred’, 500ft to go until terra firma, and we could see nothing but white clouds. The 100ft above decision came next, and there was a faint glow of approach lights up ahead, then just as the decision altitude was reached, there was a break in the low cloud/fog which allowed us to see enough of the runway to continue down to land.

I have to admit, I was fully prepared to be going around and heading to Manchester.  It’s strange how the mental process change when you know your chances of not landing are high.  Once on the ground we had the battle of finding the exit off the runway and then finding the stand before having to deice the aircraft all over again and head back to Aberdeen.

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~ by globalste on December 12, 2012.

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