Airbus near CFIT in Paris.

[kayoh190]

Keep in mind that just because an aircraft is capable doesn't mean the airline will spend the money on qualification and training. Can't speak to overseas, but I understand why the bean counters would shrug their shoulders to LPV here in the US.

 

[Spinka]

I don't know if them disconnecting the autopilot has something to do with what happened to the Airbus at the Paris air show years ago when it went into the trees. If I remember correctly, in that accident, the plane didn't respond to the TOGA because it was too low RA, so the plane was in "land mode" and wouldn't allow them to go around. I wonder if the same type of thing happened here, where the crew toggled TOGA, the plane didn't respond because of some flight control law/mode it was in, and they had to disconnect the AP to get it to go around.

You probably mean the accident at Habsheim. Land mode or not is irrelevant for the go around. If you push the thrust levers forward to to the TOGA detent you're in TOGA mode no matter what mode you were in before.
Actually even simpler and more intuitive than pushing the triggers in a Boeing. I have no idea why they disconnected the AP as it wouldn't be SOP in that situation.
As their company SOP was to increase the MDA by 50' as DA when doing an LNAV/VNAV it seems they were pretty slow in going around.

 

[MauleSkinner]

As their company SOP was to increase the MDA by 50' as DA when doing an LNAV/VNAV

I understand why companies do that with certain MDAs, but why would they do it with a DA?

 

[luvflyin]

Looks like SLS is pretty new to the 320 fleet and requires updates to the receiver (SLS needs a multi-mode receiver or MMR), updates to the autopilot as well as the flight warning computer. Also requires updates to the (Honeywell only) FMS - I guess the FMS has to be changed so the database can store and make available these type of approaches. Long story short - I bet this particular A320 did not have the upgraded SLS capability that would have allowed them to shoot the straight-in LPV approach.

SLS ??

 

[Larry in TN]

Actually even simpler and more intuitive than pushing the triggers in a Boeing. I have no idea why they disconnected the AP as it wouldn't be SOP in that situation.

Depends on the airplane and configuration.

The 737 is a fail-passive autoland system as it has only two autopilots. At 500' radar altitude, a nose-up trim input is applied, called the pre-flare, which puts the airplane is an out-of-trim condition until in the flare. At that point, you are not allowed to disengage the autopilot due to this out-of-trim condition and, if a TOGA button is pushed, the autoflight flies the go-around. If both autopilots are NOT engaged, you are not in the autoland configuration and no pre-flare trim is applied. In that case, the single autopilot is not able to perform the go-around so pressing a TOGA button will disengage the autopilot and the go-around is flown manually.

On the 757/767, and I assume the larger Boeings, you have three autopilots (left/center/right) and it does a fail-active autoland. There is no pre-flare trim. When the ILS is captures (I forget the details of the criteria), all three autopilots become active including full rudder control, in place of just the standard yaw damper. Pressing a GA paddle, at any time on the approach, will have the autopilot fly the missed approach.

I understand why companies do that with certain MDAs, but why would they do it with a DA?

They don't.

MDA's are converted into Derived Decision Altitudes (DDA) by adding 50' to the MDA. Published VNAV DAs are not changed.

 

[luvflyin]

Depends on the airplane and configuration.

The 737 is a fail-passive autoland system as it has only two autopilots. At 500' radar altitude, a nose-up trim input is applied, called the pre-flare, which puts the airplane is an out-of-trim condition until in the flare. At that point, you are not allowed to disengage the autopilot due to this out-of-trim condition and, if a TOGA button is pushed, the autoflight flies the go-around. If both autopilots are NOT engaged, you are not in the autoland configuration and no pre-flare trim is applied. In that case, the single autopilot is not able to perform the go-around so pressing a TOGA button will disengage the autopilot and the go-around is flown manually.

On the 757/767, and I assume the larger Boeings, you have three autopilots (left/center/right) and it does a fail-active autoland. There is no pre-flare trim. When the ILS is captures (I forget the details of the criteria), all three autopilots become active including full rudder control, in place of just the standard yaw damper. Pressing a GA paddle, at any time on the approach, will have the autopilot fly the missed approach.


They don't.

MDA's are converted into Derived Decision Altitudes (DDA) by adding 50' to the MDA. Published VNAV DAs are not changed.

Is that DDA mandated by FAR somehow? Or is it from Company directives? Any changes to the 50' depending on type aircraft?

 

[Larry in TN]

Is that DDA mandated by FAR somehow? Or is it from Company directives? Any changes to the 50' depending on type aircraft?

The DDA is necessary to ensure compliance with 14 CFR 91.175(c). I know of no alternate method of compliance when conducting a CDA (VNAV) non-precision approach.

You may find more information on that question in the applicable FAA ACs.

 

[Deelee]

SLS

Sorry - Satellite based Landing System. After modifications to the multimode receiver it uses GNSS + SBAS overlay for higher accuracy. It is available for retrofit on the 320. Available on the 350 and, as mentioned above, the 220. Not sure about other Airbi.

 

[MauleSkinner]

They don't.

MDA's are converted into Derived Decision Altitudes (DDA) by adding 50' to the MDA. Published VNAV DAs are not changed.

That’s what I thought, but I’ve seen that statement a couple of times with regard to this event.

The DDA is necessary to ensure compliance with 14 CFR 91.175(c). I know of no alternate method of compliance when conducting a CDA (VNAV) non-precision approach.

We have some operators who can use MDA as a DA if certain obstacle clearance criteria exist for the runway, the evidence for which shows up on the Jepp charts.

 

[kayoh190]

We have some operators who can use MDA as a DA if certain obstacle clearance criteria exist for the runway, the evidence for which shows up on the Jepp charts.

We used to do that at US Airways - the scenario was always in heavy rotation during recurrent orals. But once things married up with AA they simplified it to require the 50' addition for every MDA.

 

[luvflyin]

The DDA is necessary to ensure compliance with 14 CFR 91.175(c). I know of no alternate method of compliance when conducting a CDA (VNAV) non-precision approach.

You may find more information on that question in the applicable FAA ACs.

I'm not seeing how it is needed to comply with 175(c). You could comply with that by simply not descending below MDA. You could level off there and look for the airport. Yeah, ya gotta start arresting your descent before actually getting to MDA. But the airlines don't like that leveling off at MDA stuff. They like CDA. So they came up with the if you don't see the airport yet at that 50' above point, just treat it as a DA and miss. That's what I'm seeing about it. Is there something in 121 that explicitly addresses DDA? I guess 175 (c) (1) kinda covers it with the normal maneuvers and land in the Touchdown Zone thing.

 

[luvflyin]

That’s what I thought, but I’ve seen that statement a couple of times with regard to this event.

We have some operators who can use MDA as a DA if certain obstacle clearance criteria exist for the runway, the evidence for which shows up on the Jepp charts.

Do you have an example of a Jepp Chart about that? Just need the name of the Approach.

 

[kayoh190]

Do you have an example of a Jepp Chart about that? Just need the name of the Approach.

The common one we flew was the LOC to 31 at LGA. You can see the ball note there.

 

[flyingron]

I'm not seeing how it is needed to comply with 175(c). You could comply with that by simply not descending below MDA. You could level off there and look for the airport. Yeah, ya gotta start arresting your descent before actually getting to MDA. But the airlines don't like that leveling off at MDA stuff. They like CDA. So they came up with the if you don't see the airport yet at that 50' above point, just treat it as a DA and miss. That's what I'm seeing about it. Is there something in 121 that explicitly addresses DDA? I guess 175 (c) (1) kinda covers it with the normal maneuvers and land in the Touchdown Zone thing.

If you're in a constant descent to an MDA you're going to have to make the decision higher than the MDA so as not to bust through it on the missed. You're allowed to bust the DA provided you start the go around at the DA. The MDA gives you no leeway.

 

[luvflyin]

The common one we flew was the LOC to 31 at LGA. You can see the ball note there.

So it looks like on that one you don’t have to do the 50 foot DDA thing. You can just use MDA as a DA. If you are an authorized operator.

 

[luvflyin]

If you're in a constant descent to an MDA you're going to have to make the decision higher than the MDA so as not to bust through it on the missed. You're allowed to bust the DA provided you start the go around at the DA. The MDA gives you no leeway.

Yup. That’s what the whole discussion has been about.

 

[Larry in TN]

You could comply with that by simply not descending below MDA. You could level off there and look for the airport.

Not when you're going 130 KIAS or more. The VNAV path has you on a stabilized glidepath to the runway. Level off, look, decide, and start another descent and you aren't going to be able to land in the touchdown zone.

The ball note is an exception. Haven't seen one of those in several years.

 

[Dave Theisen]

Safe assumption that they have WAAS. ADSB essentially mandates WAAS for a position source

Not true. I’ve flown several planes that were ADS-B equipped, but not WAAS certified.

 

[kayoh190]

So it looks like on that one you don’t have to do the 50 foot DDA thing. You can just use MDA as a DA. If you are an authorized operator.

We didn't used to, and I'm sure some operators still don't. IIRC there was also some verbiage in our manual that allowed treating the MDA as a DA if there were PAPIs or VASIs to the runway. Anyway, a miss right at the 'DA' was one of the rare times where it was acceptable to end up below the charted MDA. It's now all a moot point for my airline - we add the 50 feet regardless.

 

[NoHeat]

The common one we flew was the LOC to 31 at LGA. You can see the ball note there.

What's a "ball note"?

Just wanting to learn something. I looked at the approach plate LOC RWY 31, and I didn't notice a note other than "VGSI and descent angles not coincident" on the profile view.

 

[luvflyin]

Not when you're going 130 KIAS or more. The VNAV path has you on a stabilized glidepath to the runway. Level off, look, decide, and start another descent and you aren't going to be able to land in the touchdown zone.

The ball note is an exception. Haven't seen one of those in several years.

Yup. You cherry picked my post. Here’s the whole thing again.

I'm not seeing how it is needed to comply with 175(c). You could comply with that by simply not descending below MDA. You could level off there and look for the airport. Yeah, ya gotta start arresting your descent before actually getting to MDA. But the airlines don't like that leveling off at MDA stuff. They like CDA. So they came up with the if you don't see the airport yet at that 50' above point, just treat it as a DA and miss. That's what I'm seeing about it. Is there something in 121 that explicitly addresses DDA? I guess 175 (c) (1) kinda covers it with the normal maneuvers and land in the Touchdown Zone thing.

 

[luvflyin]

What's a "ball note"?

Just wanting to learn something. I looked at the approach plate LOC RWY 31, and I didn't notice a note other than "VGSI and descent angles not coincident" on the profile view.

 

[dmspilot]

Yup. You cherry picked my post. Here’s the whole thing again.

I'm not seeing how it is needed to comply with 175(c). You could comply with that by simply not descending below MDA. You could level off there and look for the airport. Yeah, ya gotta start arresting your descent before actually getting to MDA. But the airlines don't like that leveling off at MDA stuff. They like CDA. So they came up with the if you don't see the airport yet at that 50' above point, just treat it as a DA and miss. That's what I'm seeing about it. Is there something in 121 that explicitly addresses DDA? I guess 175 (c) (1) kinda covers it with the normal maneuvers and land in the Touchdown Zone thing.

It is needed to comply with 175(c) when treating the minimums like they're a DA. We do not level off at MDA. We treat it like a DA. Therefore, a buffer is needed to prevent descending below MDA during a go-around. This is described by AC 120-108. It is not a Part 121 regulation but is part of our operations manual which ultimately must be approved by the FAA. My company uses a 75 feet addition to calculate DDA.

 

[luvflyin]

It is needed to comply with 175(c) when treating the minimums like they're a DA. We do not level off at MDA. We treat it like a DA. Therefore, a buffer is needed to prevent descending below MDA during a go-around. This is described by AC 120-108. It is not a Part 121 regulation but is part of our operations manual which ultimately must be approved by the FAA. My company uses a 75 feet addition to calculate DDA.

120-108. Thx. That’s what I was looking for. The documentation.

 

[Larry in TN]

What's a "ball note"?

The "ball note" is the note in the profile view that says, "Only authorized operators may use VNAV DA(H) in lieu of MDA(H)". It allows us to treat the published MDA as a DH which would result in descending below MDA if a missed-approach is initiated at the MDA.

Six or seven years ago I show these approaches quite a bit. More recently, it seems like more of the LNAV/VNAV minimums are published as a DA. That could be because I'm seeing more RNAV and RNP approaches and view non-precision approaches based on VHF navigation.

 

[luvflyin]

The "ball note" is the note in the profile view that says, "Only authorized operators may use VNAV DA(H) in lieu of MDA(H)". It allows us to treat the published MDA as a DH which would result in descending below MDA if a missed-approach is initiated at the MDA.

Six or seven years ago I show these approaches quite a bit. More recently, it seems like more of the LNAV/VNAV minimums are published as a DA. That could be because I'm seeing more RNAV and RNP approaches and view non-precision approaches based on VHF navigation.

What would your company’s policy be on the LOC 31 at LaGuardia?

 

[Larry in TN]

What would your company’s policy be on the LOC 31 at LaGuardia?

It has the ball note so use the published MDA as a DA.

 

[Sluggo63]

So it looks like on that one you don’t have to do the 50 foot DDA thing. You can just use MDA as a DA. If you are an authorized operator.

This MDA as DA thing is a good discussion, but not really germane to this specific incident, since AFAIK, none of that applies anywhere but in the US. I know that we can't use any of those MDA as DA exemptions outside the US (except military bases).