Crossing restrictions

gatorbuc99 said:
Just outta curiosity, what happened, wheelsup? Also, i know there are ppl alot smarter than me establishing these procedures, but aren't some stars and their crossing restrictions super inefficient? For example, the Jakie into CVG...why are jets crossing at ~13,000ft 40 miles out only for a 10,000 ft downwind and a slam dunk and then there's no one around you when you land? Or even ATL..i understand the speed restrictions 40 miles out for approach, for sequencing but why does ATC have jets start down so early when you could stay up higher longer, come down at flight idle, save a ton of gas, cross 40 miles out at oh, say FL200(just a guess), still have plenty of time to make that 10,000ft downwind...can someone enlighten me?
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Most missed crossings aren't bc pilots don't know forulas or math. It mostly bc they didn't put the info in the fms correctly, forgot to set it at all, or did all that and forgot to start down.
 
I'll make a rough stab that 50% of pilots at XJT have no idea how to use the VNAV data on the FMS.
 
Baronman said:
I'll make a rough stab that 50% of pilots at XJT have no idea how to use the VNAV data on the FMS.
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The "VNAV" that is in the EMB-145 is the most unreliable thing on that airplane. It's not a true VNAV system, you can't couple it and it'll command a 6,000 FPM descent as you come down through different layers of wind.

I'd set the VNAV and make every attempt to beat the thing to my crossing restriction. I figured if I was getting close to the carrot I had probably made a mistake and was behind on my descent.

I've seen too many guys get burned by trust that thing without doing the math.
 
The VNAV in the 145 works if you know how to work it. You have to see what is already in there, understand the presentation of "at or above" or "at or below." Certain altitudes are hard programmed into arrivals, anything that is "Cross At." Expects are not pre-programmed in.

Adding your landing rwy can mess with descent points if no prior point is in there. Why? It will think you're flying to the airport (100NM) plus flying out to some point on an approach (15NM) and then back in on the approach (15NM)...It'll think you still have 130NM to go and give you a TOD much closer than desirable.
 
VNAV on the CRJ will bite you, especially on short descents. If it's only a couple of thousand feet, and you wait till it's at 3.0 degrees, you're gonna be constantly spinning the VS wheel to catch up. On longer descents, it's normally pretty good, but it doesn't really take into account ground speed changes.

Personally, I enter it into VNAV and back it up with old fashioned math in my head.
 
jtrain609 said:
The "VNAV" that is in the EMB-145 is the most unreliable thing on that airplane. It's not a true VNAV system, you can't couple it and it'll command a 6,000 FPM descent as you come down through different layers of wind.

I'd set the VNAV and make every attempt to beat the thing to my crossing restriction. I figured if I was getting close to the carrot I had probably made a mistake and was behind on my descent.

I've seen too many guys get burned by trust that thing without doing the math.
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I always back up the FMS with mental math. However, I also use the FMS VNAV system very often for crossing restrictions. Like Baronman said, it takes a thorough knowledge of the system for it to work to your advantage. Otherwise, it will bite you in the ass.
 
Like Polar stated and Chicaga alluded to, the biggest problem we have is "uninvolved" pilots. We had a crew recently go off-route after accidently hitting the "INHIBIT" switch on the FMS. The jetway had a 30-degree course change, yet the aircraft continued going straight. 32 miles later (on the original course), ATC spoke up.

That said, EVERYONE makes mistakes. Veterans, rookies, line check airman, directors of training, you name it. The faster pilots can realize they're fallible, the better off our industry. I'm not a Kool-Aid drinker, but I'm a firm believer in threat-error management.

Everyone fails. It's how you mitigate the failures that counts.


J.
 
The VNAV in the CRJ is advisory only and it gets thrown off when you put in "Above" or "Below" altitudes.

I'll second or third the comments that it can happen to anyone. I always take out my pen and hold it when we're given a crossing restriction and decide we're not going to start down immediately. Several times I've asked myself why I've got my pen in my hand and then remembered to start down. If the workload is high or I'm very tired I'll just go ahead and start down. That may not be the best airmanship, but neither is busting a crossing restriction because we forgot to start down.
 
If the airplane won't start down for you its not true VNAV. And without ATs I don't think it would be possible
 
FlyChicaga said:
I always back up the FMS with mental math. However, I also use the FMS VNAV system very often for crossing restrictions. Like Baronman said, it takes a thorough knowledge of the system for it to work to your advantage. Otherwise, it will bite you in the ass.
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Honestly I think I use the FMS data to back up my mental math.

The single best thing we can do to help minimize altitude deviations on crossing restrictions in my opinion is to accomplish the arrival/approach brief prior to the top of descent point. Our FOM calls for this however it acknowledges this may not always be possible. In practice, I've found that our crews are a bit lazy when it comes to this even when plenty of time is available. I always give one early when flying and I ask for it early when I'm the non flying pilot.

My other personal policy is that if one pilot isn't clear on the altitude ATC has requested we verify it.

Sorry to hear about the problem Wheelsup. I'm sure it will work out.
 
EDUC8-or said:
I always take out my pen and hold it when we're given a crossing restriction and decide we're not going to start down immediately. Several times I've asked myself why I've got my pen in my hand and then remembered to start down.
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That's a good idea. I switch my watch to my other wrist when I get a crossing restriction (or actually anything else that I know I need to remember), and it seems to work pretty well--it's annoying and uncomfortable, but that's the point.

If the workload is high or I'm very tired I'll just go ahead and start down. That may not be the best airmanship, but neither is busting a crossing restriction because we forgot to start down.
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:yeahthat:

I've flown with Captain Lets Save Every Drop of Gas who starts down when there's a 3500'/min rate required only to get hosed by getting slowed or changing winds (usually the same guy who taxis single engine at ORD when the it's clear the taxi's going to be short). It's not worth the couple dollars in fuel savings to have to stress about making a crossing.
 
zmiller4 said:
That's a good idea. I switch my watch to my other wrist when I get a crossing restriction (or actually anything else that I know I need to remember), and it seems to work pretty well--it's annoying and uncomfortable, but that's the point.


:yeahthat:

I've flown with Captain Lets Save Every Drop of Gas who starts down when there's a 3500'/min rate required only to get hosed by getting slowed or changing winds (usually the same guy who taxis single engine at ORD when the it's clear the taxi's going to be short). It's not worth the couple dollars in fuel savings to have to stress about making a crossing.
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I like the watch idea. As far as waiting until the absolute last minute to start down or rushing FO's on the ground there's no need for that. I usually try to be a "Company Guy" but making things interesting and exciting on a routine flight is totally unnecessary.
 
EDUC8-or said:
I usually try to be a "Company Guy" but making things interesting and exciting on a routine flight is totally unnecessary.
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Those are my sentiments exactly. If it's a matter of 2-6 thousand feet, I'm not going to sweat while watching the crossing fix "disappear below the nose." Late at night when ATC starts offering PD to the MVA in the approach area from your cruise altitude, I'm all about idle thrust descents and spooling up on a 5-mile final.

There are way too many mitigating factors that effect fuel burn to worry about a 2,000 foot crossing restriction. Our operation recently published average hourly fuel flows for the previous month. The spread was from around 2,700 to 3,000 (CRJ-200)... only 300 pounds of variance, which, considering the diversity in our flying (segment length ranges from 100NM-1,000NM), isn't much.

The real waste for us in on the lead-in line waiting for marshalers. 16 pounds a minute with all three turbines running.
 
EDUC8-or said:
If the workload is high or I'm very tired I'll just go ahead and start down. That may not be the best airmanship, but neither is busting a crossing restriction because we forgot to start down.
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I do the same thing. Sometimes I'm just too exhausted to do math and to remember to start down so I just do it early. I miss doing idle power descents in the ERJ.

Kinda funny, in my interview for my current job flying the Beech 1900, they interviewer asked what I could do to save fuel. I mentioned that I always try to do idle power descents. He just kinda giggled at me. Now I know why. Idle power descent in the Beech is awfully exciting for the guy in 9B!
 
The Dash-8 "ghetto FMS" VNAV worked well enough that I rarely had to worry about it. Or maybe it worked so poorly that we monitored it well enough that it didn't seem to matter. You plug in cruising altitude and the altitude you want to cross fix at and it gives you a mile/time to TOD and then a required FPM down and puts it in your glideslope.

You just roll the descent in and if it starts going out of the glideslope, roll more in. *shrugs* I always put fix-2 miles so I had a 2 mile buffer.
 
zmiller4 said:
That's a good idea. I switch my watch to my other wrist when I get a crossing restriction (or actually anything else that I know I need to remember), and it seems to work pretty well--it's annoying and uncomfortable, but that's the point.
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That's what I used to do to remind myself to close VFR flight plans. Worked every time.
 
Sometimes for piece of mind I'll just start the descent right away... like if it's an ATC-requested crossing restriction.
 
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