Do you ccept the FMC descent prediction or over-ride it?

[cliffardus 3]

In Captain Ray’s amusing book “737NG Training Syllabus : Simulator and Checkride” he notes that “…..the computer will usually make a prediction that will probably see you HIGH and FAST on your approach to the airport.”

 

What has your experience has taught you?

 

Do you over-ride the FMC Flight Plan by using “V/S” and “VL CHG” and later, if necessary, “SPD INTV” and SPEED?

 

Or do you trust in the FMC to bring you in safely as planned?

 

Cliff

[Airbusman330 300]

I often override the FMC for various reasons but the biggest thing to make sure is that your altitude restrictions are correct and as this is being typed I had to correct a restriction for my descent via the ROYKO3 into ORD, chart calls for a plane to cross LOOTH at 11,000 however the FMC had me crossing it at FL340.

[Yosm 19]

A lot of times on manual. With flight level change button. Mostly due to traffic or just out of exprrience with the airport and runway.

Final approach mostly manual

[Andrea1 6]

Hi Cliff,

depends on a lot of factors: gusting winds, speed altitude restrictions atc requests etc tec. On the other hand YOU are the pilot, YOU are the captain you must decide and "think ahead" your plane...if you would accept always the automatics you wouldn't be a pilot...but just a "system observer"...

 

Ciao

 

Andrea B.

[Tabs 2,790]

Use of VNAV in the terminal environment (aside from RNAV approaches and stuff like that) is actually relatively rare in the real world. It's way easier to reach up and hit LVL CHG and HDG SEL to comply with an unexpected ATC instruction than it is to sit there attempting to figure out how to program what they just gave you into the FMC. There's a reason those modes exist in the AP system and this is it...

[KriVa 307]

http://www.youtube.com/watch?v=h3kREPMzMLk

[dmncnpilot 39]

Tabs and KriVa hit it right on the head. In cruise flight you have the time and luxury of programming and inputing into the fms, however in the terminal area it's a whole different ball game. Sometimes it's just better and safe to disengage the AP and hand fly to make that restriction or the atc instruction.

[cliffardus 3]

These responses confirmed my gut feeling that I should  rely on myself first and the AP second.

 

But it's not ruddy easy...........he/she's meant to be so much cleverer than us............

 

Cliff

[KriVa 307]

Not really... It's only as clever as the numbers that are fed into it.

GIGO (Garbage In, Garbage Out) is the rule with any computer. And while humans are very flexible and can think very dynamically, a ciomputer can't. That's why the past few years, there has been quite a lot of discussion on getting pilots back in the habit of flying their planes, instead of typing in numbers and letters.

[P50andpilot 7]

I often override the FMC for various reasons but the biggest thing to make sure is that your altitude restrictions are correct and as this is being typed I had to correct a restriction for my descent via the ROYKO3 into ORD, chart calls for a plane to cross LOOTH at 11,000 however the FMC had me crossing it at FL340.

This is because that is an expected crossing not a descend via arrival. The FMC will provide the most efficient descent and that keeps you higher than most arrivals.

 

11000 will only be entered once assigned.

 

 

Sent from my iPhone using Tapatalk 2

[Airbusman330 300]

This is because that is an expected crossing not a descend via arrival. The FMC will provide the most efficient descent and that keeps you higher than most arrivals.

 

Yea but I sure did not find it efficient, if I followed the FMC then I would have had one heck of a time trying to descend and slow down in time to meet the localizer at a reasonable altitude while the chart game me a nice gentile continuous descent, plus the -800 is a bit slippery. 

[Simul8 2]

You can only do a gentile descent while eating a Bacon Sandwich.

 

Using all of the tools available... VNav, LVL Chg, VS and the speed brake, you'll always be able to get her down, and slowed up sufficiently to make the approach, the trick as always is to be ahead of the aircraft. As with many of the previous posts, remember always that the FMC will always do what it's told. It is unable to think critically, or indeed at all.

[cavaricooper 2,615]

Gents- I'd refer you to a very wise Mr. Bill Bulfer. When in the descent/approach phase, with various headings and level-offs to accommodate a busy ATC environment, the TACTICAL modes are best. Heads up, eyeballs on a swivel and HDG SEL and LVL CHG. When in the less frenetic phases of flight, the STRATEGIC mode or the FMC is preferred.

 

That said, as a single pilot, your workload can get much higher than that of a well rehearsed a flight crew with excellent CRM skills so USE WHAT IS APPROPRIATE for the particular situation.... Even a bit of manual flight every now and then (the FPV is your friend).

 

That said, on a late evening approach, where one has entered all the STAR altitude and speed restrictions, descent winds, temp deviation and pressure, AND VNAV IS NOT RUINED BY SHORTCUTS- the FMC does an admirable job of taking the NG from LNAV/VNAV to LOC/APP. When you can do this with your CFMs just spooling up as you select Gear Down/Flaps 15.... It's a beautiful thing.

 

She's lovely... and will only get better

[dmncnpilot 39]

Airspace is too congested :( unless you fly for a cargo company and fly in the reverse side of the clock.

[scandinavian13 5,192]

I just want to add in a quick note from a procedural side, related to ATC:

 

While the Navigraph data has an inconsistent approach to the data (I have no experience with the other providers), there are two different types of (US) STARs that you'll see.  One is a profile STAR, which will have set altitudes that you must cross AT, AT OR ABOVE, or AT OR BELOW.  These are shown as altitudes with bars above and below (AT), bars below (AT OR ABOVE), or bars above (AT OR BELOW).  When you see these, they will not be accompanied by the word 'expect.'  These altitudes will normally be set in the nav data.

 

The other type is not profile based (generally older A-nav* STARs, before VNAV became more commonplace) and usually contains at least one note of "expect [altitude]" and occasionally a speed as well.  These expect entries may or may not be in the data, and it would be a best practice to verify it is there.  Even if it's just to expect it, get the automation ready to aim for that altitude.  If the controller changes it, it will likely only be by a couple thousand feet, but they will generally give the differing altitude with enough time to adjust (and throw it in the automation for number crunching).

 

If you do not check the altitude and it is not in there, the automation will miss it every time.  What's invisible to pilots and most others is why those entries are there.  A notable example is the LENDY6 into JFK (which the automation hates, because of a 250/FL190 restriction only 20nm from the airport).  I've written several posts about it, so I'll leave it out here, but the point to take away is that the automation only has a clear of a picture as you give to it, and even then you may not fully understand the picture (which means it has even less of a clue).  As such, dispense with VNAV as soon as it becomes more of a pest than a help.  VS is of more use in the terminal environment in most cases (after finishing profile STARs of course).

 

*A-Nav is a term we use to denote procedures able to be flown by the simpler modes of navigation (/A being the code for DME and Mode C only).  It essentially means "those incapable of RNAV procedures."