Julesmusician From , joined Dec 1969, posts, RR: Posted (10 years 5 days 21 hours ago) and read 6708 times:
Question arising from the fact that the UK has been fogged out for a lot of airports yesterday and today. BA just cancelled all their regional flights which I find amazing, I thought we were in technology now that allows foggy landings.
The question is:
If the prediction at the destination airport is for severe fog which is below minimums set for your aircraft - are you allowed to "go have a look" - I mean by that is going into the approach in case it turns out clearer than predicted or is it usual that the flight will be cancelled? Just having a look at the airports that were affected - BA cancelled the regional flights, Easyjet managed to land all their aircraft so there must be substantial different operating criteria for the aircraft - sounds like the airports are all equipped with the necessary, just the aircraft are not. I was always of the belief you could fly to the destination and then see what the current visibility is and if it doesn't work out choose a diversion.
Oly720man From United Kingdom, joined May 2004, 7075 posts, RR: 11
Reply 1, posted (10 years 5 days 21 hours ago) and read 6691 times:
Incoming aircraft will either hang around until the minima are exceeded and divert when fuel levels get low or divert straight away if the weather's too bad/ doesn't look like getting better. I don't think pilots will risk an approach on the offchance that the weather will improve by the time they get to the airport because an approach and go around is more risky than orbiting a beacon, possibly in bright blue skies above all the fog.
The RVRs are not predicted they are measured with instruments along the runway so ATC knows immediately what the touchdown/midpoint and stop end visibilities are.
Departing aircraft won't depart because if there's an emergency they may not be able to land again.
A lot of BA's regionals were on the EMB145 which may not have the same minima as other aircraft such as the A3xx and B737s of EZY.
The reason for cancellations was probably because the inbound aircraft had diverted and the logistics of getting all the outbound PAX to the other airports was not worth the effort/risk, especially given the road conditions.
Could the diverted aircraft have flown out empty to their next destination to return and possibly divert again when they came back and have even more PAX to ferry about in coaches?
VuelingAirbus From Spain, joined Aug 2005, 113 posts, RR: 1
Reply 3, posted (10 years 5 days 21 hours ago) and read 6685 times:
Well - i don't want to get too much into detail but landing in fog (so called CAT2/3 - Approaches) depend on many factors. The crew has to trained and have a valid endorsment in their licence and the aircraft has to be equipped. Both is costly and the smaller the airline and the smaller the type operated the less chance you have that the managment would do it. For CAT 3 you need two independent autopilots (might be replaced by a head up display) and autothrust... its just not worth for a regional airline. Plus there is another consideration. The approach spacing has to be much higher than under visual conditions (the tower cant see you and you would interfeer with the ILS signals for the traffic behind you if the spacing is to close). That means that the capacity which a runway can handle goes down a lot. Which aircraft would you divert? A 747 or a CRJ? hope that helped...
Technically i have to disagree. Under certain circumstances there is a look and see. Lets say the field reports fog patches and the RVR varies and I start a CAT 2 approach. I get constant RVR messurments but beyond the OM I can continue and "look and see" even if the RVR goes down below minima. The result would be a go around at 100 feet if I dont have visual references but in that case I did look and see. However - I am not allowed to start the approach in the first place if the conditions are reported to be below the minima applicable to the approach I intend to do....
Bellerophon From United Kingdom, joined May 2002, 586 posts, RR: 58
Reply 6, posted (10 years 5 days 19 hours ago) and read 6647 times:
...beyond the OM I can continue and "look and see" even if the RVR goes down below minima...
Yes you may, but technically the RVR cannot go down below minima after passing the OM, because any RVR given after passing the OM is advisory only, and does not affect the legality of the approach.
The last RVR received on approach before the OM is the relevant RVR for deciding whether or not you may legally continue that approach beyond the OM down to DH.
As you say in your example, if the last RVR passed to you before the OM is above your limits, you may continue down to DH, even if, once beyond the OM, further advisory RVR reports suggest the RVR has deteriorated below limits.
However, this is not a "look and see" approach. The last official RVR was above your limits, and the approach therefore is perfectly legal.
Other than in an emergency, there is no occasion when you may legally continue an approach beyond the OM, down to DH, when the relevant RVR for that approach is below your minima.
CosmicCruiser From United States of America, joined Feb 2005, 2267 posts, RR: 15
Reply 9, posted (10 years 5 days 18 hours ago) and read 6612 times:
Quoting Bellerophon (Reply 6): Yes you may, but technically the RVR cannot go down below minima after passing the OM, because any RVR given after passing the OM is advisory only, and does not affect the legality of the approach.
I must disagree at least for the U.S. FAR 121.651 (c) says that the capt. may continue the approach below MDA,DA or DH and land provided the a/c is in a position to land in the touchdown zone making a normal rate of descent AND The flight visibility is NOT LESS than the minimums for the approach procedure.
TDZ RVR is always controlling for CAT I, II and III. MID and R/O may be required and advisory only or not required at all for CAT I & II. CAT III TDZ MID and R/O are required and controlling with R/O adv.; RVR less than 600'(175m) then all 3 are controlling.
According to our ops man. even in foreign countries that allow "Look See" approachs (beginning or continuing an app. with below mins wx.) we are not allowed to do it.
Usnseallt82 From United States of America, joined Jan 2004, 4891 posts, RR: 51
Reply 10, posted (10 years 5 days 18 hours ago) and read 6606 times:
Quoting Oly720man (Reply 1): The RVRs are not predicted they are measured with instruments along the runway so ATC knows immediately what the touchdown/midpoint and stop end visibilities are.
Exactly right. RVR's are instant readings from the runways that tell exactly what the visibility is. There is always the chance that things could clear up before the next RVR is posted, but the tower will always know the immediate conditions. If the RVR is calling for below mins, chances are it isn't going to improve significantly when you arrive. You can always contact ATC to get an updated reading, but if that's below mins then you're better off to divert.
Also, be aware that most airlines hold rules and regulations for these types of circumstances that are more stringent than the federal regs. You may be able to legally land in certain conditions, but it may be against your company's specific regs. This may be the difference between the EasyJet flights and BA Regional ones. Regardless, unless you are experiencing some sort of emergency on board, it is best not to test the accuracy of the RVR readings by having a 'look see.' You may be able to do it legally, but I'm pretty sure your company would have a shit fit if they knew what you were doing.
Julesmusician From , joined Dec 1969, posts, RR:
Reply 11, posted (10 years 5 days 18 hours ago) and read 6592 times:
Thanks for this. It just seems strange that if the 737's etc of Easyjet can get in without problem, and BA's Emb's cannot, then that will be remembered by business travellers. Since the majority of regional work by BA to Europe appears to be buisness passengers I would argue, this is a route that BA should be investing substancially in. It only takes someone with a brain at Easyjet to publicise the fact that if you want to go regional, take them as they will get in. Some airports in the UK suffer a lot from fog. I can just see a newspaper advert from Easyjet showing BA up.
I assume that BA probably coached their pax to London as their network was so big they could get them out through their main hub.
As for the technical side of things, I assume that you would be in constant contact with air traffic and they would be updating you every minute with visibility. What I can't understand is why GPS isn't used much more in close approaches. The accuracy now is incredible down to a few metres, which is certainly enough to get in real close to see if you can see. You know the height of the runway so it should be straight forward. Maybe GPS just isn't considered good enough or stable enough. With two or three GPS units cross checking each other I reckon the accuracy would be near on 100%.
Thanks for the information so far, of great interest.
Julesmusician From , joined Dec 1969, posts, RR:
Reply 14, posted (10 years 5 days 13 hours ago) and read 6484 times:
Can the pilots answer - when you are doing a fog approach do you have to declare to Air Traffic what Cat you aircraft and your pilots is approved for? Or is that your own business they will just give you information...The other thing is the mix of different measurement units. On the one hand we have km and metres then on RVR are the METARS in feet?
Is this RVR of 250ft or 250 Metres? I assume the 0200 is general visibility in metres...
Below is a quote from a previous forum post about categories and landing decisions for any people who aren't aware of the different Cat landing standards...
Quoting 747Teach Mirrodie: Some operators have been authorized to operate certain aircraft into reduced weather minimums. These carriers have a program called the Lower Landing Minimums (LLM) to keep their operations in compliance with the FAA rules. Basically, three separate functions must occur to be legal to operate in reduced weather minimums. The aircraft must have the required equipment, certified and in working order, the airport must have the required equipment, certified and in working order, and the crews must be trained and certified to fly into those conditions.
The LLM program allows operation of aircraft into very low visibility weather conditions. The factors controlling the minimum runway visual range (RVR) and decision height (DH) within which a pilot-in-command may conduct an approach and landing are based on the operational status of several aircraft systems and their components.
The catagories you are asking about are described as follows:
Category 1: An instrument approach procedure which provides for approaches to a decision height of not less than 200 feet and visibility of not less than 1/2 mile or RVR of 2400 feet (RVR of 1800 feet with operative touchdown zone and runway centerline lights).
Category 2: An instrument approach procedure which provides approaches to minimum of less than DH 200 feet/RVR 2400 feet to as low as DH 100 feet/RVR 1200 feet.
Category 3a: A precision instrument approach and landing with no decision height (DH), or DH below 100 feet, and controlling runway visual range not less than 700 feet.
Category 3b: A precision instrument approach and landing with no DH, or with a DH below 50 feet, and controlling runway visual range less than 700 feet, but not less than 150 feet.
Category 3c: A precision instrument approach and landing with no DH and no runway visual range limitation.
As you can imagine, not all operators choose to operate their aircraft into all of these conditions. The initial cost of the equipment, and the cost of maintaining that equipment, could be considerable. Many airports do not have the required equipment installed for the same reason. The cost of training and keeping aircrews current could be very high. The cost of not having all of these factors in compliance is increased diversions. In many cases, operators do not feel the additional cost outweighs the increased chance of diversions.
FAA Advisory Circular 120-28C dated 3-9-84 may be of use to you as reference. Regards,
Pihero From France, joined Jan 2005, 5011 posts, RR: 78
Reply 16, posted (10 years 5 days 12 hours ago) and read 6457 times:
Hi, Jules !
Quoting Julesmusician (Reply 14): when you are doing a fog approach do you have to declare to Air Traffic what Cat you aircraft and your pilots is approved for?
Low visibility procedures (LVP) are broadcasted on the ATIS. It is then up to the crews to check their minima and decide whether they could attempt an autoland or hold or divert. Normally each operator has submitted their minima to the airport authorities. If found that you landed below your minima, You and your airline will be in dire trouble.
Quoting Julesmusician (Reply 14): The other thing is the mix of different measurement units. On the one hand we have km and metres then on RVR are the METARS in feet?
As per ICAO recommendations, the visibility -or for precision approaches, the Runway Visual Range (RVR) - is given in meters.Some countries, including the USA prefer the statute mile and feet .Still according to ICAO standards, they should add SM or FT at the end of the vis data.But it is not done all the time.
Your example therefore reds as this :
EGSS:22.20Z observation :wind :350°/2knots;visibility 200meters;RVR runway O5:250 m ; RVR Runway 23 :275 m ; FOG ; ceiling unavailable ; temperature and dew point : 3°c ; QNH 1039 hp.
Julesmusician From , joined Dec 1969, posts, RR:
Reply 17, posted (10 years 5 days 12 hours ago) and read 6451 times:
Thanks for that, so my previous post on the RVR in feet is for the category divisions, but the actual METAR is in metres. How do you know if they are in ft or metres - is it made clear on the METAR or do you have to guess depending on where you are? (you say it is not done all the time in the US for example)
The interesting question is starting an approach - it seems you must be told that the RVR is at least to the category you are ok for before you can even turn onto finals and descend. I find that strange in that all the way down you are likely to be in fog, and as you descend the visibility may increase and allow you touchdown - however the arguments put forward about a go around in fog being much less preferable than holding is a good one.
My answer was based on the WX prior to crossing the FAF or G/S intercept altitude. Once you're inside those points, it can go to 0/0 and you can still land.
At most airlines I've been associated with, if the WX is below your minimums once you arrive, you don't have the option of a "look see" even if it's authorized in that specific location. Usually, the liability issues outweigh any possible benefits.
Pihero From France, joined Jan 2005, 5011 posts, RR: 78
Reply 20, posted (10 years 5 days 12 hours ago) and read 6435 times:
Quoting PhilSquares (Reply 18): At most airlines I've been associated with, if the WX is below your minimums once you arrive, you don't have the option of a "look see" even if it's authorized in that specific location. Usually, the liability issues outweigh any possible benefits.
ShyFlyer From , joined Dec 1969, posts, RR:
Reply 21, posted (10 years 5 days 10 hours ago) and read 6392 times:
Quoting Usnseallt82 (Reply 12): GPS is still not considered precision approach though. It may be extremely accurate these days...
Actually, with WAAS, GPS has the ability to meet CAT I minimums. These types of approaches are not yet in widespread use, however.
I'm surprised no one has mentioned Horizon and thier use of HUDs, or just HUDs in general. I remember reading somewhere (and I'll be darned now that I can't find it) that Horizon use of HUDs get them in an out of foggy airports when everyone else is on the ground. Can't remember the specifics though.
OPNLguy From , joined Dec 1969, posts, RR:
Reply 23, posted (10 years 5 days 8 hours ago) and read 6370 times:
Quoting ShyFlyer (Reply 21): I'm surprised no one has mentioned Horizon and thier use of HUDs, or just HUDs in general. I remember reading somewhere (and I'll be darned now that I can't find it) that Horizon use of HUDs get them in an out of foggy airports when everyone else is on the ground. Can't remember the specifics though.
Me also. Now that all the 737-200s, our entire 737 fleet (-300s, -500s, and -700s, 441 in all) have HGS, and we hand-fly approaches down to CAT-IIIa (RVR700). Takeoff mins are 1/4SM RVR1600, or RVR600/600/600 (depending upon what's installed at the airport), and on SEA 16R we can depart with RVR300.
Jspitfire From Canada, joined Feb 2005, 309 posts, RR: 2
Reply 24, posted (10 years 5 days 8 hours ago) and read 6368 times:
The Vancouver area has had really dense fog for the past 3 days, and I think YVR has only gone up to 1/2 SM vis a couple times. It has usually said either 1/8 or 0 SM. Because this fog was forecast, and they know that it will be there for the entire day, most flights that could not do an approach or takeoff were cancelled before they left. The float planes and Helijet have not been doing flights between downtown Victoria and Vancouver either due to the fog.
It has been a bit weird though...I do my flight training in Abbotsford, which for those that know the area, isn't too far from Vancouver. The entire Fraser Valley has been covered in Fog, but Abbotsford has remained clear every day. It works well for us if we're just flying around the airport, but we can't go anywhere else!
: As has been mentioned, GPS isn't really good enough yet. Systems with a combination of GPS and airport beacons are being tested, that would allow ops
: OPNLguy ... In the UK, there are no such things as "takeoff alternates?"... Yes. JAR-OPS 1.295(b) A take-off alternate must be specified, and annotate
: A/C with HUD have lower visibility minimums don't they? The Sorcerer
: Good, that should put this statement to rest:
: They vary from country to country Low Visibility Operations and in particular CAT II/III equipment represent a significant cost for an airline. The h
: Julesmusician, I wouldn’t count on EasyJet always landing in foggy conditions. On Monday, my flight to Bristol-Berlin flight was cancelled because t
: Yes and no. Same thing but two different concepts. I a conventional jet you have the throttles to control thrust and if the automation takes over thi
: The question that has arisen is on landing/take off - how do you actually keep the aircraft on the centre line if you can't see anything?
: on take off you have a minimum rvr for take off (125 m) to see the runway center line lights (cause its done manual) and during CAT3c with 0/0 you hav