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Topic: "Air Canada Too Low On Approach" In NYC
Username: YYZatcboy
Posted 2012-12-13 22:20:58 and read 8595 times.

http://www.thestar.com/news/canada/p...o-low-too-soon-in-new-york-landing

An air traffic controller had to alert the pilots of an Air Canada flight after they descended too low during a bad weather approach to New York’s La Guardia airport.

The airline has launched an internal probe into the Nov. 27 incident involving Air Canada Flight 748, which happened as the twin-engine Embraer 170 jet was arriving from Montreal.






Anyone know what exactly happened? Was it an erronious altitude alert from ATC or did the pilots descend below their clearance?

Topic: RE: "Air Canada Too Low On Approach" In NYC
Username: keuleatr72
Posted 2012-12-13 22:42:44 and read 8514 times.

The incident was reported last week by the avherald:

http://avherald.com/h?article=45a21558&opt=0

Topic: RE: "Air Canada Too Low On Approach" In NYC
Username: DualQual
Posted 2012-12-14 08:37:01 and read 7490 times.

I've gotten a "Too low" alert from tower while doing a practice NDB in VFR as a dive and drive and we were above all crossing restrictions. It's possible that if they were doing a non-precision that does not have VNAV guidance as a dive and drive they might have hit a spot that whatever sets off the alarms in ATC without violating any crossings.

Topic: RE: "Air Canada Too Low On Approach" In NYC
Username: Viscount724
Posted 2012-12-14 08:40:58 and read 7377 times.

Quoting keuleatr72 (Reply 1):
The incident was reported last week by the avherald:

http://avherald.com/h?article=45a215...opt=0

As with many of the Avherald reports involving Canada, it's almost a verbatim copy from the Transport Canada occurrence report.

Topic: RE: "Air Canada Too Low On Approach" In NYC
Username: longhauler
Posted 2012-12-14 09:00:02 and read 6794 times.

Quoting DualQual (Reply 2):
they might have hit a spot that whatever sets off the alarms in ATC without violating any crossings.

No, this definitley was an error.

The aircraft was instructed to be no lower than 1700' until DNNIS, on the RNAV - LNAV/VNAV approach. One mile outside DNNIS they were at 1000' and descending with the autopilot engaged and the approach armed, thus the (accurate) warning from ATC.

It is being investigated internally, with TC assisting. The two major areas of the investigation are:

1) With the autopilot engaged, and the approach armed and functioning, why was the aircraft at 1000' and descending?

2) When things were clearly not going as planned, why did the crew not intervene?

When warned, the crew did normal SOP, in that they did a go-around, climbed up to a safe altitude and re-evaluated the cause for the loss of situational awareness.

Topic: RE: "Air Canada Too Low On Approach" In NYC
Username: rampbro
Posted 2012-12-14 09:16:56 and read 6306 times.

Quoting keuleatr72 (Reply 1):
The incident was reported last week by the avherald:

http://avherald.com/h?article=45a215...opt=0

There is one heck of a cat fight going on in the comments on that avherald posting  

Topic: RE: "Air Canada Too Low On Approach" In NYC
Username: longhauler
Posted 2012-12-14 09:42:36 and read 5539 times.

Quoting rampbro (Reply 5):
There is one heck of a cat fight going on in the comments on that avherald posting

Yes, and very few are about the actual incident!

Topic: RE: "Air Canada Too Low On Approach" In NYC
Username: flylku
Posted 2012-12-14 09:44:38 and read 5470 times.

With all the automation today there is still the potential for deviations. That said, the system works.

Topic: RE: "Air Canada Too Low On Approach" In NYC
Username: Aesma
Posted 2012-12-14 12:27:24 and read 5122 times.

I was just reading the basics on coupled approaches yesterday. Could they have inputted 700 feet instead of 1700 ?

Topic: RE: "Air Canada Too Low On Approach" In NYC
Username: longhauler
Posted 2012-12-14 13:03:04 and read 5098 times.

Quoting Aesma (Reply 8):
Could they have inputted 700 feet instead of 1700 ?

No. The only time vertical navigation can be used is if the approach from the FAF to the runway is unaltered, and exactly as stored in the FMS. So no altitudes would have been entered or changed. (And your example would be a reason why this SOP exists.)

Topic: RE: "Air Canada Too Low On Approach" In NYC
Username: mmedford
Posted 2012-12-14 20:59:06 and read 4895 times.

Might want to double check this... but Runway 4 ILS @ LGA might have been NOTAM'ed out...during that incident.

Topic: RE: "Air Canada Too Low On Approach" In NYC
Username: Dogbreath
Posted 2012-12-14 23:21:19 and read 4834 times.

Quoting longhauler (Reply 4):
No, this definitley was an error.

The aircraft was instructed to be no lower than 1700' until DNNIS, on the RNAV - LNAV/VNAV approach. One mile outside DNNIS they were at 1000' and descending with the autopilot engaged and the approach armed, thus the (accurate) warning from ATC.

I agree.

Without actual facts as to what was happening within the flightdeck, but with the known facts as reported at AVherald, it may indicate a loss of situational awareness by the crew as to where they were on the approach.
I'd also be interested to know if they had the correct QNH setting. Not sure how the Embraer FMC logic calculates it's descent path solution for a GPS VNAV approach, but it might calculate an incorrect descent path with an incorrect QNH.
Mind you a 700 foot QNH error is pretty unusual.

Look forward to reading the incident report, whenever it's released.

Topic: RE: "Air Canada Too Low On Approach" In NYC
Username: Mir
Posted 2012-12-15 07:34:58 and read 4683 times.

Quoting Aesma (Reply 8):
I was just reading the basics on coupled approaches yesterday. Could they have inputted 700 feet instead of 1700 ?

If they tried to input the altitude at DNNIS into the FMS after being given the crossing restriction and missed inputting the 1, it might be possible depending on the avionics setup. But 1700 is the specified altitude at DNNIS on the approach already, so there should have been no need to do that.

I can't speak to any company prohibitions against altering navigation fixes in the database - I'm sure there are some, but I don't know the specifics.

-Mir

Topic: RE: "Air Canada Too Low On Approach" In NYC
Username: longhauler
Posted 2012-12-15 07:55:07 and read 4672 times.

Quoting Mir (Reply 12):
I can't speak to any company prohibitions against altering navigation fixes in the database - I'm sure there are some, but I don't know the specifics.

I don't know whether that restriction is a Company SOP, or a Transport Canada requirement when licencing for GPS RNAV approaches.

Basically, the SOP is that for Vertical Nav to be used down to a DH, all of the altitudes in the FMS from the FAF to the runway can not be changed. The only time one would change an altitude is for temperature correction. But ... in the E175/E190 that is not necessary, as it does temperature corrections itself ... so the FMS can change an altitude, just not he pilot!

In older aircraft like the B767 or the A320 where temperature corrections are manual, then the vertical nav (or profile in the Airbus) portion of the approach can not be used.

Topic: RE: "Air Canada Too Low On Approach" In NYC
Username: Mir
Posted 2012-12-15 09:28:55 and read 4621 times.

Quoting longhauler (Reply 13):
Basically, the SOP is that for Vertical Nav to be used down to a DH, all of the altitudes in the FMS from the FAF to the runway can not be changed.

I assume that includes the FAF?

Also, since the LNAV minimums are lower in this case than the LNAV/VNAV minimums (by six feet, but still), would it be possible that they decided to not use the VNAV function? Because the profile described is consistent with the airplane aiming for DNNIS at 700 instead of 1700 - I'm just trying to figure out if there's a rational explanation for that or whether it's just coincidence.

-Mir

Topic: RE: "Air Canada Too Low On Approach" In NYC
Username: BE77
Posted 2012-12-15 09:48:45 and read 4612 times.

What about something as simple as the wrong altimeter setting?

Topic: RE: "Air Canada Too Low On Approach" In NYC
Username: longhauler
Posted 2012-12-15 10:11:17 and read 4605 times.

Quoting mmedford (Reply 10):
but Runway 4 ILS @ LGA might have been NOTAM'ed out

Which would explain why they were doing an RNAV approach instead of the ILS.

Quoting BE77 (Reply 15):
What about something as simple as the wrong altimeter setting?

Anything is possible, but I think this might be unlikely simply because of the SOP 3 cross checks between the set altimeter settings and the printed ATIS, including one where the PNF actually points to the altimeter setting on the ATIS, then points to what is set to the PF. In this case, it would have to be an inch out. Again, possible, but unlikely.

Quoting Mir (Reply 14):
LNAV/VNAV minimums (by six feet, but still), would it be possible that they decided to not use the VNAV function?

I think pilots are basically lazy, (I know I am) for the sake of 6 feet I think they would opt for a fully coupled approach, right down to 50'. But in this case, because the LNAV/VNAV minimum is a DA, we can use it, because the LNAV is an MDA, we have to add 50'!

In Canada, the only non-precision approaches we can do are what are termed "Constant Descent Angle" approaches. The old days of diving down to MDA then waiting and timing are no longer performed. So, an FPA would have to be set going by DNNIS, in this case 3 degrees. At MDA+50 either land or go-around. It is probably just easier to do the LNAV/VNAV and leave it coupled to 50'.

Topic: RE: "Air Canada Too Low On Approach" In NYC
Username: Aesma
Posted 2012-12-15 12:59:45 and read 4544 times.

Quoting longhauler (Reply 9):
No. The only time vertical navigation can be used is if the approach from the FAF to the runway is unaltered, and exactly as stored in the FMS. So no altitudes would have been entered or changed. (And your example would be a reason why this SOP exists.)

Yeah, what I read was geared to GA and sunday flight simmers, it didn't include FMS. I guess computers do make life duller !

Topic: RE: "Air Canada Too Low On Approach" In NYC
Username: YYZatcboy
Posted 2012-12-22 01:10:07 and read 3791 times.

It has now happened again....

http://www.thestar.com/news/canada/p...-runway-too-low-triggering-warning

AC has apparently told its pilots to not do the RNAV to 04 in LGA. Faulty Database? I would have thought that the crews should still be verifying their altitudes, but I don't know AC's SOP's regarding RNAV approaches and verification.

I'm now really curious to see what is going on, and why if it's a database issue it has not happened more often.

Topic: RE: "Air Canada Too Low On Approach" In NYC
Username: Dogbreath
Posted 2012-12-22 01:49:19 and read 3781 times.

If that report is true then, I must say I'm deeply shocked that two separate crews have blindly followed a VNAV approach without cross reference to the charted approach plates (charts). If there is a database error, then during the descent and approach set-up, and briefing, the incorrect waypoint crossing heights, would have surely been discovered and manually changed to comply with the approach. Also during the actual approaches the flight crew should be monitoring the approach to ensure correct compliance with the descent profile. Just sitting there and blindly following the FMC database to minima would be in-excuseable. You may as well be sitting aft of the flight deck door with the passengers.

I'm assuming that a great number of other AC crews have flown this approach without any incidents, so why these two? If other crews had flown with the same database, then is there a reporting system in AC that highlights database errors. We have in my Company, and any errors are immediately dealt with by contacting the relevant departments concerned for a database review and/or update, and immediately alerting all flight crew members.

Topic: RE: "Air Canada Too Low On Approach" In NYC
Username: longhauler
Posted 2012-12-22 09:00:25 and read 3703 times.

Quoting Dogbreath (Reply 19):
If that report is true then, I must say I'm deeply shocked that two separate crews have blindly followed a VNAV approach without cross reference to the charted approach plates (charts).

It has now been 4 times in the last two weeks! Two requiring ATC intervention, as noted.

Funny you mention the "cross reference", as that is actually the problem. There is nothing to cross reference against, as it is a stand alone GPS RNAV/LNAV/VNAV approach, with no ground based information to cross reference. And ... it appears that may be where the error occurs, in the actual database construction of the approach.

Quoting Dogbreath (Reply 19):
I'm assuming that a great number of other AC crews have flown this approach without any incidents, so why these two?

All of these incidents have occurred since the last database update, so not only Air Canada and Transport Canada, but Jeppesen and Embraer are involved as well. Curiously, it only occurs on the E175, not the E190. So you would have to look at how many E175s have done an approach into LGA in the last two weeks, only on Runway 4, and only when the ILS is off the air (for cross reference). It makes me think ... only 4!

Topic: RE: "Air Canada Too Low On Approach" In NYC
Username: Mir
Posted 2012-12-22 12:51:01 and read 3657 times.

Quoting longhauler (Reply 20):
Funny you mention the "cross reference", as that is actually the problem. There is nothing to cross reference against, as it is a stand alone GPS RNAV/LNAV/VNAV approach, with no ground based information to cross reference.

I believe he's talking about cross-referencing the waypoints in the FMS (and their corresponding altitudes) against what's published on the chart.

-Mir

Topic: RE: "Air Canada Too Low On Approach" In NYC
Username: longhauler
Posted 2012-12-22 13:19:06 and read 3649 times.

Quoting Mir (Reply 21):
I believe he's talking about cross-referencing the waypoints in the FMS (and their corresponding altitudes) against what's published on the chart.

Yes, but in a database error, the waypoints may not be in the right position.

Topic: RE: "Air Canada Too Low On Approach" In NYC
Username: Mir
Posted 2012-12-22 18:45:40 and read 3525 times.

Quoting longhauler (Reply 22):
Yes, but in a database error, the waypoints may not be in the right position.

Shouldn't matter. Every GPS system I've seen prohibits modifying approaches. So if I look at an approach and the altitudes don't match what's on the chart, my only option is to decline the approach. I don't know whether it's because the waypoints aren't in the right position or whether someone coded the altitude incorrectly, but the result is the same: I'll have to find another approach to fly.

-Mir

Topic: RE: "Air Canada Too Low On Approach" In NYC
Username: Dogbreath
Posted 2012-12-23 02:15:19 and read 3434 times.

Quoting longhauler (Reply 20):
Funny you mention the "cross reference", as that is actually the problem. There is nothing to cross reference against, as it is a stand alone GPS RNAV/LNAV/VNAV approach, with no ground based information to cross reference. And ... it appears that may be where the error occurs, in the actual database construction of the approach.

I don't fly with CA or on the Embraer. Nor have I flown into La Guardia for a long, long time. However having had a look at the RNAV (GPS) Y approach into La Guardia's runway 04, it has specific waypoints on the approach. Ponae at 12 miles with a not below restriction of 3000ft, and Dnnis at 5 miles with a not below restriction of 1700ft.
The FMC will have these waypoints coded into the GPS approach, with the altitude restrictions. You are correct in that these are not ground based navaid waypoints but are GPS waypoints. Could these waypoints have been incorrectly located? It's possible, but again with cross-referencing the approach chart to the FMC during the descent and approach briefing this should and would have been picked up. I don't doubt the aircraft flew the LNAV tracks as per the approach, as ATC would have picked them up on being off track, it's just the descent path that is in question here.

Quoting Mir (Reply 23):
Every GPS system I've seen prohibits modifying approaches.

On my companies FMC's we can only change the altitude restriction, and not the actual waypoint position. Especially important for cold weather altitude corrections below 0 degree C. So if the database had an incorrect altitude crossing restriction, we can and would amend it.

But as you correctly say if in doubt about the integrity of the FMC's approach data, then fly another approach type.

Topic: RE: "Air Canada Too Low On Approach" In NYC
Username: longhauler
Posted 2012-12-23 08:00:32 and read 3472 times.

Quoting Mir (Reply 23):

I get what you are saying, and the investigation continues. The pilots have been exonerated in all occurrences.

Now ... imagine the database error is that the entire approach string is in the wrong location! Remember, you have no ground based back up!

Quoting Dogbreath (Reply 24):
But as you correctly say if in doubt about the integrity of the FMC's approach data, then fly another approach type.

Yes, or do what they did in all occurrences. Pull up, go around, rethink things from a safer altitude.

Topic: RE: "Air Canada Too Low On Approach" In NYC
Username: pilotpip
Posted 2012-12-23 11:50:05 and read 3404 times.

Quoting longhauler (Reply 16):
Quoting mmedford (Reply 10):
but Runway 4 ILS @ LGA might have been NOTAM'ed out

Which would explain why they were doing an RNAV approach instead of the ILS.

The approach and lighting systems at LGA were damaged pretty bad during Sandy. 22 was down for a couple weeks but is now back up and normal. 4 isn't used as much during the summer and fall but with the weather the last few weeks it's become more frequent.

I've done more non precision approaches there in the past two months than I've done in my career combined.


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