The difference is that with speed off the A/T might come forward due to Min Speed Reversion if they were not designed to retard. So the feature is not there "in case you forgot to retard", it is implemented because of what I've written in bold.

A/T come off 2s after touch down.

BTW, no single channel to touch down, right?

The only allowed possibility to touchdown with A/T armed, other than dual channel, is speed off, A/P off, right?

• The AT is a complementary system to the AP and may be used with or without the AP.
• The 737 is certificated for autoland using dual APs; the AT, if engaged, will retard at 27ft.
• The 737 is also certificated for single AP approach to a minimum approach altitude (80 ft … cert authorities/737 versions may differ). The AP has to be disengaged for landing, but the AT may remain engaged and will retard at 27ft. Presumably this option enables a single AP MEL auto approach.
• If a pilot elects to fly a manual approach with AT, it may remain engaged and will retard at 27 ft.

Why have so many AT options … ? Because over the years pilots thought that it would be a good idea – it reduced workload, made life easy, wouldn’t it be nice if … etc, etc, and Boeing attempted to satisfy the widest possible market and retain a good MEL – which is also operator driven.
It appears that it is the method of interfacing the inputs and components of the FGS to provide these options, which has left a loophole in operations in the event of malfunction (but not necessarily for a failure).
You can keep some of the people happy all of the time, but … … … and that’s the point where opportunity for mistakes, misinformation, and false knowledge arises.

Speed reversion is an alternative pitch mode providing limited protection from abnormal low speed. It is normally engaged automatically from another mode. It is not available from GS.
GS mode is a AP ‘path on elevator’ mode, where the AT controls the selected speed datum. A speed reversion would require AP ‘speed on elevator’ mode, where a climb or descent is determined by the thrust setting. Reversion from GS would require a high thrust setting to ensure a climb. This logic is already built into the TOGA mode which provides a pitch up and an AP ‘speed on elevator’ climb, commanding the appropriate thrust setting on the AT.
Speed reversion is not an Airbus 'alpha floor' type of function, which is a higher order safety protection and operates independently of the AP/AT.

If someone wanted to end the thread on a high note,this would be it.Clear,concise explanation.

safetypee:

Presumably this option also assumes a correctly functioning RA#1 with no redundancy?

Ok, RB, got it! In your B738 there is no separate autoland "A/L" or "APPR" selector in order for the A/P [and A/T] to do full autoland. Understood.

Downin3Green - couldn't agree with you more!!! Right on. Nowadays, those things that stick out of the center quadrant, often referred to as thrust levers, or throttles, really should be renamed as hand rests!

Pending release of further info from the investigators may I respectfully request that this thread be temporarily locked.

It would:
a. permit many (most) to read all the current posts;
b. stop the circular arguments.

As a former Tower controller, I do wonder what I might have said to a pilot with decreasing ground speed (well below what one would have previously seen or might reasonably expect at that stage of flight).

Faulty RA
 

This is what the MEL states, and why in retrospect it is important to check this even before commencing, or even to execute a missed approach, to get the full picture with respect to downgraded equipment on an A/C. As most pilots does`t know the contents of the MEL by recall/Memory.

:With radio altimeter(s) inoperative, do not use the associated autopilot or Autothrottle for
approach and landing.


Still we do not know if this particulare fault had been adressed by the flight crew in this accident before or during the approach. It might even been this fault that had pussled them, and taken their attention away.

Norwegian - you are way off the rails. They were NOT using the associated autopilot. There is no restriction in the MEL to which I am attuned to use of autothrottle. Perhaps there should be, although it would not have affected this accident since the radalt was not an MEL item.

You don't get it, SC, do you? It was NOT an MEL item. Read the thread. In this case the MEL is not relevant.

Even if it had been, you above all should know that an MEL is company specific and some NG MELs say

3. With radio altimeter(s) inoperative, do not use the associated autopilot for approach and landing.

Note the missing bit! There's a job you should get your teeth into.

missy

I believe this has been mentioned earlier, however it assumes that you have little else to do other than physically watch ever single arrival. Surely at an airfield such as EHAM this is just not feasable.

Out of interest what would have you said? , bearing in mind it may further confuse an already confused and disorientated cockpit.

Rainboe:

Simple question: Why do we have MSAW?

Ah Sorry! Of course, you have no idea what MSAW is! It's NOT the controllers job to fly the aircraft. Hence, MSAW is unknown to you, or forgotten because it's a very, very silly system).

Let me refresh you memory (either you like it or not):

MSAW=Minimum Safe Altitude Warning systems

From SKYbrary - MSAW i quote:

Minimum Safe Altitude Warning (MSAW) is a ground-based safety net function of an ATC radar data processing system. MSAW is intended to assist in the prevention of controlled flight into terrain accidents by generating, in a timely manner, an alert of a potential or actual infringement of a minimum safe altitude. The MSAW function, using software in ATC computers, alerts ATCOs when radar returns indicate an aircraft penetrating or about to penetrate the minimum safe altitude.

--End of quote--

MSAW is of course a total waste of money as the ATC operator is not supposed to fly or tell the pilots how to fly. Go figure! Heck, the next they'll come up with is MSSW (Minimum Safe Speed Warning).

SC Let's, at least, get this right.

ARINC 707-6 Document Information: Title, Radio Altimeter. Aeronautical Radio Inc. Publication Date: Oct 30, 1998

And this, typical -

1. PRODUCT OVERVIEW
The ALA-52B Radio Altimeter (RALT), designed and manufactured by Honeywell’s Aerospace Electronics Systems. The ALA-52B RALT, a lightweight, solid-state, airborne altimeter provides accurate digital height measurements above terrain during aircraft approach, landing, and climb-out phases. The operating range is –20 feet to +8000 feet.


http://www.honeywellcommnav.com/docu...l/52b_tech.pdf

SC :ugh: I suspect that I've installed, from scratch, more RadAlts than you. The zero reading should be seen with oleos extended, bogies in trail, and the trailing wheels just touching. Understand?

When we have finished redesigning the Radio Alt. we had better turn our attention to the Auto Throttle. If it had malfunctioned in such a way that it set a low RPM or throttle closed the result would have been the same.

Things fail – We usually sort the problem. (Usually, since there is no denying that a wing coming off would be challenging) This was a case where there really wasn’t much of a problem to sort. SOPs/Standard calls should have taken care of it. (Assuming that the sequence of events was as reported.)


Yes I have read the whole thing

Each autopilot requires its own radio altimeter by design requirements. They are independent sensors linked to their own autopilot and are not allowed to be crossfed into other autopilots.
Also rad alts can have a negative reading on the ground. They are calibrated to read zero when the main landing gear contacts the runway in the landing configuration. Once the aircraft settles on the ground and the landing gear oleos are compressed, you will have a negative reading.

Takeoff: LNAV is available and commonly selected above 400'RA. Ist clue.
In descent "2500" EGPWS call from RA. 2nd clue.
On finals "1000" call from RA.

I think all these come from LHS RA. There may be different customer options for call outs, but the RA can be seen to be in use before the final approach. There might not be a u/s flag, but there are various scenarios where it can be seen to be correct yes/no. If so, is the concentrating on lack of tech log entry being so significant not a slightly smelly fish.

Maximum and biggles225, I am so glad you have got your coats. Could you kindly persuade most of the other posters here to get theirs as well, so that the Mods can lock the door behind them and the rest of us can have a proper discussion on how 3 pretty experienced pilots can fly an aircraft, with no major defects, into the ground and kill themselves. Thank You.

Too Many Straws
 

We all have heard of the straw the broke the camel's back. This appears to be another case of too many straws:

Rushed approach in IMC.

Turned onto final approach above glidepath, requiring throttle-off descent.

Radalt #1 locks onto false signal path and puts out -8 feet, valid.

GPWS sounds off with "Too Low, Gear", due to radalt #1.

Capt. EADI displays -8 feet, probably in a yellow meatball.

AT goes unnoticed into Retard mode, the throttles already pulled back in dispatched descent to catch the glidepath.

What we don't know yet is the "conversation" and other distractions being loaded onto the PF's brain as well, to the point he fails to react to decaying airspeed.

GB