Autoland question
 

I was thinking about this on my way into work this morning (maybe it was the dull grey weather...)

Last year a Singapore Airlines T7 ended up off the runway at Munich following what appeared to be a bodged autoland without the full protections in place. Basic explanations of ILS systems state that there are effectively 2 parts to the ILS array on the ground - the localiser beams, spread horizontally to line the aircraft up with the runway centreline, and the glideslope beams, spread vertically. It is implied (if not stated) that these are located are the near end of the runway you are approaching.

My question is - in the case of an autoland, what happens once you have passed over the near end of the runway? The Munich incident shows (I believe, and the fact that protections need to be in place to perform a full autoland) that the AP is still locked onto a localiser of some sort to guide it down the runway (rather than a pure heading, otherwise interference wouldn't be an issue, right?). So does the localiser at the near end have something that points down the runway as well or is there another one at the far end for an autoland capable runway? Same goes for the glideslope - my instinct would be that once the aircraft has passing over the G/S beam at the near end the AP will know the runway length and its own actual altitude AGL from the radio altimeter and can therefore calculate what it needs to do in terms of V/S from that? If so is that part of what makes an aircraft have an autoland capability above the AP just being able to follow the localiser and G/S?

Also, is it/can it be a full hands-off operation right to the point of being stationary on the runway ie does it apply reverse thrust and brakes?

Thanks

The localiser antenna is always at the FAR end of the runway. If there is also one at the near end, that's for use when landing in the opposite direction.

http://atcsl.tripod.com/Images/ils-layout.jpg

As I understand it, some a/c can run to a stop with full braking and others can get to the ground and throttle back - but then need the brakes to be applied. I sit to be corrected.

The brakes on the A320 are automatic, and can be selected to LOW or MED depending on runway and conditions. They work very well with autobrake, but my company has no restriction on using manual brakes (pilot operated) if required (perhaps if we were expecting to roll to the far end.

The reversers are selected by the pilot, although during an automatic landing, the power is automatically reduced to idle as the aircraft flares for landing.

DH

Glideslope transmitter is beside the runway abeam touchdown zone, say 300 m in. So the loaliser tracks the aircraft to touchdown and beyond and the glideslope to the touchdown zone. Any significant deviation on a CAT III approach sohuld lead to a go around.

"the power is automatically reduced to idle as the aircraft flares for landing."

Really, on the A320 series I thought it still shouted retard at you at about 30 feet. Otherwise, with the thrust levers in the normal flight position, (the climb detent on the throttle quadrant), when the weight comes on the wheels, the logic changes to ground mode from flight mode, and power is controlled by thrust lever angle, not autothrust. And you would get plenty.

My, limited, understanding is, for a full autoland, the crew still need to, :}activate the approach on the fms or overfly the pseuodo approach way point, ensure the correct runway and approach is in the box, ensure ils is tuned and identified, ensure managed nav and speed, arm approach mode, arm autobrake, select flap and gear as required, make sure nothing fails on the way down, retard the thrust levers, reverse thrust, make sure the aicraft is slowing, disconnect autopilot at 70 knots on the roll out, cancel reverse, manual braking, find the correct exit from the runway, reconfigure for the taxi in and grope your way to yhe terminal without hitting anything.

Low vis ops are a real pain.

During a manually flown landing the auto callout comes at 20ft.

During an autoland the callout comes at 10ft, and is a reminder for the pilot to close the thrust levers. However, the thrust will have automatically reduced to idle by this stage.

DH

On the approach (B757/767) the pitch attitude (controlled by the elevators) is adjusted by the autopilot as required to follow the glideslope. At flare height (20 ft) the pitch control input switches from glideslope to radio altimeter. The autothrottle simultaneously retards the thrust levers to idle. At touchdown the localiser input is switched from the roll channel (controlled by the ailerons) to the rudder to correct potential centreline deviation. Reverse thrust is manually selected. Wheel braking is auto or manual.

Further info on autoland and low vis ops is available from (paperback or Kindle)