ddressel

set missed approach altitude in MCP

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hi everyboby,

I´ve a problem setting the MAA.

I´m flying an RNAV approach Milano Malpensa Rwy 35L, as described in the FCOM page 144.

MDA set to 1100 ft

MAA=4000 ft

1100 is set in the MCP

Reaching 1700-1600 ft (300 ft below the MAA) and setting the MAA to 4000 ft, VNAVpth changes to VNValt and the Acft climbs again.

Whats wrong?

Dieter Dressel

 

 

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hi everyboby,

I´ve a problem setting the MAA.

I´m flying an RNAV approach Milano Malpensa Rwy 35L, as described in the FCOM page 144.

MDA set to 1100 ft

MAA=4000 ft

1100 ft is set in the MCP

Reaching 1700-1600 ft (300 ft below the MAA) and setting the MAA to 4000 ft, VNAVpth changes to VNValt and the Acft climbs again.

When I set the MCP back to 1100 ft I´m back descending and VNAVpth

Whats wrong?

Dieter Dressel

 

 

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Dieter,

I suspect you have been following the technique as described in the Boeing diagram 'Instrument Approach Using VNAV' - unfortunately I cannot post a copy of the diagram here for fear of a copyright strike, you should be able to find a copy of it in the QRH document under the Manoeuvres Chapter Flight Patterns, or in the Flight Crew Training Manual Chapter 5.41.

There is a 'gotcha' in these diagrams, the assumption is that you will have already crossed the FAF (Final Approach Fix) & the FMA will have 'annunciated' SPD - VNAV PTH

After you have crossed the FAF you should have the aircraft fully configured for landing & as such with the FMA indicating as above you will be able to press the MCP SPD Button & open the MCP SPD window to dial in the VAPP Speed (normally VREF +5kts).

The FMS has transitioned into the 'on approach' logic allowing the aircraft to perform the vertical segment of the approach down to your MDA.  Please remember that the 744 is now almost 30 years old, it cannot perform this type of approach to the degree of accuracy that a 737NG or a 777 can.  The 744 only transitions into the 'on approach' logic after crossing the FAF & only if the MCP ALT is set to an altitude lower than that required at the FAF.

If you are fully configured BEFORE the FAF & you try to 'open' the MCP SPD 'window' in the 744 you will get SPD - VNAV SPD 'annunciated' on the FMA, the aircraft will fly away from the PTH & you may well blow the approach, as such & since you have NOT PASSED the FAF, if you set the MCP ALT to the missed APP ALT (which might be higher than the FAF crossing height) the aircraft will catch VNAV ALT since you are asking it to do something else.

So to recacap, look at the diagram, follow the procedure & ONLY set missed approach altitude ONCE you have crossed the FAF & you have SPD - VNAV PTH 'annunciated' on the FMA. 

Remember that in the 744 the vertical guidance takes the aircraft down to an imaginary point 50ft above the runway threshold, you must have the autopilot & autothrottle disconnected at or above your DA(H) or MDA(H)

An easy way to find out where the FMS will transition to the 'on approach' logic is to look into the LEGS Pages, find the first WPT in the approach sequence where the glidepath angle is displayed (normally 3.00), this is where the 'on approach' logic should commence, in the 744 it is normally the FAF.  Obviously do this as part of the pre descent preparations, before your T/D so you are well prepared.

You can monitor the performance of the FMS Position Accuracy whilst you are conducting the approach by putting one of the pilots CDUs onto the POS REF Page 2/3.  Look at LSK3L & monitor the RNP/ACTUAL number.  The 'on approach' logic will require an RNP of 0.3 of a NM & your actual must be at or less than this number for you to continue with the approach.  This is is the only visual indication other than an EICAS Caution Message coupled with a 'beeper' sound cautioning you that your ANP does not meet the accuracy criteria required during the approach phase.  There are no RNP/ANP scales drawn on the PFD as seen on the PFDs in the 737NG, 777 or 747-8.

Since the PMDG iteration of the 744 does not use the ARINC formatted navigation data I am not sure if this is correctly simulated but it is worth a try.

Finally don't forget, its a 29 year old aircraft that had twin GPS added at a later date, its a second generation glass flight deck, more advanced than the 767, but in comparison to the 737NG & the 777 its now very dated.  It cannot perform these types of approaches to the degree of accuracy that the newer aircraft can.

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3 hours ago, G-CIVA said:

The FMS has transitioned into the 'on approach' logic allowing the aircraft to perform the vertical segment of the approach down to your MDA.  Please remember that the 744 is now almost 30 years old, it cannot perform this type of approach to the degree of accuracy that a 737NG or a 777 can.  The 744 only transitions into the 'on approach' logic after crossing the FAF & only if the MCP ALT is set to an altitude lower than that required at the FAF.

If you are fully configured BEFORE the FAF & you try to 'open' the MCP SPD 'window' in the 744 you will get SPD - VNAV SPD 'annunciated' on the FMA, the aircraft will fly away from the PTH & you may well blow the approach, as such & since you have NOT PASSED the FAF, if you set the MCP ALT to the missed APP ALT (which might be higher than the FAF crossing height) the aircraft will catch VNAV ALT since you are asking it to do something else.

I agree with most of what you are saying Steve, but I disagree with your premise that because the 400 is 30 years old, it is less accurate than the 777 or 737NG. Early jets that used DME-DME Updating only as the highest form of position updating would have been less accurate, but jets with dual GPS would have virtually no difference in the accuracy of the ANP, which is normally like .02 for an RNAV Approach requiring .3 RNP in the 400. Pretty darn accurate...

Also SPD - VNAV SPD, is not a possible FMA combination, you can't have speed controlling both pitch and thrust at the same time. The FMA would be IDLE - VNAV SPD, and then change to HOLD - VNAV SPD.

Most of the time On Approach logic commences well before the FAF, one of the criteria for on approach logic is to select a published instrument approach and that the airplane has sequenced the first waypoint on the published approach. Procedurally, once your past the FAF and more than 300 feet below the missed approach altitude, you can set the missed approach altitude.

 

 

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Agreed, re IDLE - VNAV SPD I was actually away from my books & on a tablet at the the time so hence the error, apologies, I normally cross check & refer to them as a write.

The point I was trying to emphasize was the 'gotcha' of attempting to set the Missed Approach Altitude BEFORE crossing the FAF, simmers may miss this vital step when looking at the Boeing diagram & it is a common source of errors.

I'll slightly disagree with you on the navigation capability of the 744 compared to its more recent brethren, RNP is purely a measure of LATERAL accuracy surely?

The newer aircraft have the capability to navigate in the vertical sense without reference to ground based navigation aids to a higher degree of accuracy than the B744, which is the point I was also trying to make, the 737NG & 777, 787 & 747-8 are all IAN capable, the 744 is not.

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hi Steve,

thanks for the help, I have the diagramm but didn´t saw the relationship between FAF and MAA

I will try...

Dieter Dressel

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OK, now that you are talking IAN Steve, I agree with you...

We were talking strictly VNAV, but now that you include IAN, I concur...

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hi Steve, tried the approach as you described and shown in the diagramm.

EDDK 14L, TRANS NOR, set MDA 710 ft, reached the FAF LEGDU an 3000 ft. After passing LEGDU and descending set MAA to 2000 ft: rising up.

Tried it several times, everytime the same, even when I´m below DA

Will try at other airports, maybe there is still a pilot error...

Dieter Dressel

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Dieter, just to be sure, you DID load the RNAV approach & not the ILS approach (I am not trying to insult your intelligence BTW).  Try the procedure as you say at some other ARPTs, it should work with SPD - VNAV PTH & speed intervention after the FAF.  If this is not successful then I guess the only course of action is to raise a support ticket.

Alexander, this is the trouble with forum chatter, its like being deaf & communicating with a time delay.  Now we have met on the same page!  Amongst simmers there is an assumption that one Boeing is much like another, as you know this is not the case.

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hi Steve,

I found this in the former PMDG 747-400 X manual 10_PROCEDURES_PROFILES_747_400_V10, NON PRECISION APPROACHES:

"When passing the MDA, set the missed approach altitude into the MCP altitude command bug in order to minimize workload in the event of a missed approach." (page 12)

But the diagramm at page 16 is the same as the new one in the QRH.

Curios....

I will try again....

Dieter

 

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hi Steve,

OMG, as I thought (and maybe you too): pilot error!!

1. Wasn´t fully configured for landing.

2. Setting MDA in the MCP, but didn´t press (how stupid)

Had a few landings at KLAX RNAV Y 07L, working fine,

What do mean with "speed intervention" after FAF. I try to have Vref at the FAF.

Thanks for your patience.

Dieter Dressel

EDQK

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1 hour ago, ddressel said:

What do mean with "speed intervention" after FAF

It means you press the MCP SPEED button and use the window to set target speed, instead of FMS doing it as in VNAV mode; however, inside the FAF (I thought it was IAF) you can have both VNAV and MCP SPD.

 

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