ILS Approach, flare?

[Krallu]

Hello!

How do you know when to start the flare, and power cut off when doing an ILS approach?

Let's say that the visibility is zero or almost zero, how to not descend it straight into the runway?

Do you look at the radio altimeter, is the radio altimeter a requirement then?

What about smaller planes without radio altimeter?

Thanks!

[buttline]

Krallu,
If you're talking about handflying jet on an ILS in visual conditions, at approx 30-50ft above the ground (radio alt) the pilot will close the thrust levels and pitch up just a few degrees for the touchdown. On light aircraft, you pull back on the stick much more.

When the weather is zero,zero (eg Fog), it is not permitted to fly the approach manually and a landing can be only be done using the aircraft's full Autoland capability. For this both nav boxes must be tuned to the ILS freq and both autopilots must be engaged. The a/c will do the flare and touchdown and track the runway centreline but the pilot must apply reverse thrust, apply the brakes (or autobrakes) and handle the roll out.

[Krallu]

Ok thanks a lot for that information. So it is based on the radio altitude when to start the flare.

So is a radio altimeter a requirement to do ILS landings? I'm now thinking about smaller aircrafts. Are they approved to do ILS landings without buying an expensive radio altimeter. Or is there a limit that you need radio altimeter for CAT II and CAT III but not for CATI or something like that?

Thanks a lot!

[carbonfibre]

Krallu,

To fly a light aircraft in the conditions you are suggesting is not allowed anyway without a visual cue from the point you hit your instrument approach minima which lets just say it is 200 ft for an IR rated pilot and 50ft PEC.

You must be able to make a confiramtion that you can make the runway (ie lead in light, runway lights etc) and at 200ft you should see something, as buttline has said anything else requires specific equipment, training and aircraft to do the zero vis approach.

Besides you would have probably not made an approach and diverted anyway:ok:

[Krallu]

Oh thanks! Now I can see it a little more clear.

Just a fun tought.

What are you pilots doing if you are in the situation where it is CATIIIc (0-0) and you are not approved to do that sort of landing, and you can't divert you need to land there, due to let's say fuel or something like that.

Anyone have experience fo soemthing like that, or how do you react? You fly the approach anyway and do your best?

Or it doesn't have to be CATIIIb it can be a little more less than your or your plane is approved for.

Just a tought.

[slingsby]

If your weather is zero visibilty at the destination, you wouldn't go anywhere near the airport let alone try an approach. Yes, the aircraft having CAT3B landing capabilites can land in zero visibilty, but why would you when you can't see where to taxi to, or worse case what you may hit on the runway...
Why hand fly an ILS in low visibility when you can let the autopilot do the work for you.
If you have no option and diversion not available (bad call if you've let it get this bad) then your aircraft can land wherever you decide. However saying that, most airfields will close if their visiblity is less than 75m, this is to enable the emergency services to find you if you stuff it in. So if the Vis is getting close to minimum, you would have decided long before reaching the terminal area, what your options are and you nearest available divert airport.

I have landed with RVRs of 75m, and then spent 40 minutes taxing to the gate as we couldn't see the taxiway lights from the cockpit, yes we even opened the window to look down to see if we were still on the tarmac at one point. When we finally found our stand (with marshall and ATC assistance), we could only see about 10m outside the cockpit. We questioned the tower for their RVR accuracy, and were informed the vis was now less than 50m and the airport was closed.

[FlightDetent]

What are you pilots doing if you are in the situation where it is CATIIIc (0-0) and you are not approved to do that sort of landing, and you can't divert you need to land there, due to let's say fuel or something like that.

Unless we speak of a complicated emergency plot, you are referring to a situation where the only alternative left would fail. What we are paid to do is to never have only one single alternative left, so - that is what we do.

In the other case, whenever in emergency (oh silly my, like I've ever had one:rolleyes: ) there is no more we can do than our best including full utilization of equipment and resources available. :ok:

Let's take the everpresent common CATIIIa (50ft/200m) autoland capable 737 as an example:

Apart from other important gadgets, you have an ILS reciever to give you guidance, you have FlightDirector/Autopilot system to follow the guidance with sufficient precision and flare, and you have the radioltimeter to replace the ILS's vertical guidance below 50' where it no longer provides usable data. The machine has dual installations of these, say A&B.
Of course you need someone to retard the throttles. That can be the autothrottle (one installed) or the pilot flying (two installed, one active at the time which will be always the captain mostly due to human performance and legal issues).

A and B being independent systems, they cannot differentiate which is right if either one goes astray until the moment when the difference is so great both system trip off. Given the velocities, heights and widths, you NEED the captain to look outside and asses whether A&B are correct, which takes place at or above 50 ft (go decision) or anytime until the reversers are unlocked (no go decision). In order to do this (i.e. assess position and flightpath with reference to runway environment) you need some amount of flight visibility and a great deal of lighting close below. But the only thing you may/must do then is to retard the throttle or intiate/fly a go-around.
Upon touchdown A&B disconnect and the aircraft is quasi-manually brought to a stop.

It can be seen that having A&B+C is a key requirement for 0ft/200m operations and that ability to follow lateral ILS guidance after touch-down is essential for 0/0 capability.

To summarize, there's a great world of differece between safe operations (MAY) and solved emegergency (CAN). In my eyes CAN = capability + check, MAY = CAN + proof. As far as autolands go, having only two independent systems doesn't constitute grounds for safe operations.

[Krallu]

OK I see. There is enough equipment to solve that sort of situation even if you can't divert.

Of course divert is the best option.

Thanks for helping me clear my mind. Looking forward to taking my IR and trying at a beginning litte more worse weather than just VFR.

[GearDoor]

You think that is bad, try doing a single-pilot circling approach to a remote airfield in the middle of the night in poor vis. Definately not saying that it is more difficult, just a different type of IFR challenge.

[pilot_will]

The A320 calling out "Retard" (close thrust levers) is quite handy. With some autolands's I do on flight sim, the aircraft seems to forget to flaire! So I need to ask for the front wheels to be changed and the suspension to be checked! :)

[john_tullamarine]

I think that it's useful to distinguish between

(a) what makes good sense from a real world risk mitigation point of view (low vis procedures are based on multiple autopilots and autoland or HUD/FD/EVS etc.) and

(b) what is a useful stick and rudder I/F skills development exercise in the sim (raw data, hand flown, ILS to a full stop in 0/0 conditions - and it doesn't take much work during an endorsement program to get people up to this standard)

Of course one can do a little bit of practice and develop the I/F manipulative skills to do (b) - it's good fun, great for the ego, and does improve the push and pull skills out of sight.

But ... in the real world ... the consequences of a mistake, or subtle systems failure are such that (a) makes a whole lot more sense.

[pigboat]

Heh, heh Geardoor, it would seem you've done a few of those Down East International approaches. :D