It looks like that KKE17 fix has the wrong airspeed. Just delete that 250 or put 210 and it should work.

It looks like that KKE17 fix has the wrong airspeed. Just delete that 250 or put 210 and it should work.

 

While I agree to this and I wouldn't let the aircraft accelerate to 250 for right after having to slow down to 210 (I don't think that's a good practice, during climb I always try to accelerate and never have to slow down),

 

Why isn't the FMC even "trying" to reduce after passing KKE17? The commanded "FMC SPD" on the speedtape is stuck at 250, he doesn't put it down to 210 to try and comply with the speed restriction, which, by the way, could be met without adding speedbrakes: 6nm to reduce from 250 to 210, should work on leveled flight.

Brilliant guys honest appreciate your work! Just don't know why the FMC doesn't reduce speed !!!

I just looked at the SID. The old link died, so I tracked down the new one.

 

This is an odd departure. I've never seen one where you accelerated and then decelerated. Maybe something in the FMC prevents it from decelerating in the climb. Dunno.

 

Just to check, you did select the SID in the DEP/ARR page, correct? You didn't just select the fixes.

 

You could change the 250 to 250B and the 210 to 210B, like Enrico said several posts ago. I'm not sure how pilots would handle this RW. I've never seen a SID like this.

 

Thanks for bringing this one up. It's interesting.

This is due to the way the FMC calculates routes, speeds, and altitudes.

On ascent, it won't let you slow down or go down. It will always expect the next waypoint on your route to be either at the same level and speed, or higher and faster. (Or, of course, a combination of those.)

On descent, it won't let you go up or speed up. The next waypoint always has to be either at the same level and altitude, or lower and slower. Or, again, a combination of those. (Same level but slower, lower but same speed,...)

Again, this is how the FMC calculates it. That does NOT mean you can't override that behaviour, just by dropping a level in automation.

For example, you want to go slower on your way to the next waypoint while climbing out? Sure, just drop down a level of automation: go from LNAV to LVL CHG, or even straight down to SPEED and V/S.

 

I know there is a specific term for this kind of behaviour, but it escapes me now.

This is due to the way the FMC calculates routes, speeds, and altitudes.

On ascent, it won't let you slow down or go down.

 

Makes sense to me. Thanks!

 

I didn't know the FMC wouldn't let you slow down, because I've honestly never tried to slow down during a departure!

Makes sense to me too !!

 

How will i know when to select the speed or input it into the FMC when approaching these waypoints? Don't want to be too early or is that just good skill and judgment of the PF?

If you check the sids/ stars of  the approach plate of  the airport your landing it will tell you what alt/speed you need to be at  these waypoints

 

http://www.ead.eurocontrol.int/eadbasic/pamslight-33B12BA68E335C04C5B90825E3534676/7FE5QZZF3FXUS/EN/Charts/AD/AIRAC/EG_AD_2_EGKK_6-21_en_2014-04-03.pdf

 

https://www.youtube.com/watch?v=nJ7c-02va_g  ( 4  parts )

 

 

 

There good training  videos around on hows these are done  just a matter of  googling  the net  and you will find  them,  even Kyle  has  done  a few on these

 

 

How will i know when to select the speed or input it into the FMC when approaching these waypoints? Don't want to be too early or is that just good skill and judgment of the PF?

 

You should always keep your speed at or below the restriction until AFTER passing the waypoint. During the SID, if there's a speed limit at some point of 210, never exceed those 210kts prior to that point. During climb your speed always goes up. During descent your speed always goes down.

 

Also make sure you always review your LEGS page on the ground and compare it to the chart. That's something you must do in real life too.

 

Very important: The FMC is NOT a replacement for the charts.

Brilliant guys honest appreciate your work! Just don't know why the FMC doesn't reduce speed !!!

 

Hello Vernon,

 

I had a through check on that SID. The numbers you are giving us are correct: max 250 kts on the first three waypoints, and then max 210 kts till Big vor. I flew this SID a couple of times, trying different things, and this is what you can do to meet the speed requirements:

 

1) On the ground, you just arm LNAV, and leave the speeds as they are in the FMC. The FMC will tell you "unable 250 kts at xxx or unable 210 kts at yyy, do nothing on the FMC. When you are airborne, you engage LNAV e CMD A on the MCP. You'll notice the speed in the MCP increases to V2 + 20 kts, and since you did not engage VNAV, the aircraft will maintain that speed in the MCP speed window. I had a V2 of 146 kts, and the speed moved up to 166 kts. If you do nothing till BIG vor, the aircraft will keep holding that 166 kt speed, of course you increase it to flaps 1 or flaps up, by turning the speed dial. You are now flying in LNAV and MCP SPEED, that is what it reads on the FMA, in green letters. Once you reach the flaps 1 speed, you can hold it till BIG, or you can increase it to UP speed, and raise the flaps. The UP speed should be around 210/220 kts, well, keep it like that till KKE17, and right at KKE17 lower the speed to 210 kts. Bear in mind that the Boeing 737 NG needs about 1 nm distance to lose 10 kts of speed...

 

2) On the ground you change all the speed limits in the FMC by adding a B, as I told you yesterday. After take off, you engage both LNAV and VNAV. You'll see that now the aircraft will stay within the 250 kts limit, till KKE17, but after that waypoint it won't slow down, it will tell you "unable 210 kts at KKE23". At this point, you hit the LVL CHG switch, and lower the speed to 210 kts, and you are all set.

 

As you see, in both cases you have eventually to intervene manually to lower the speed. Which procedure you use is up to you, I prefer the first one, as it gives me immediate control over the speed and I do not have to change anything in the FMC.

 

Now try them both, and let us know how it goes, have fun!

 

Enrico :smile:

Ok on the ground i can't select LNAV or VNAV but after takeoff i can? I have set up the FMC correctly.

Vernon

 

What are your departure and arrival airports plus runways for this flight you are working on?

 

Thank you

Michael Cubine

Enrico what a legend !!! Will try it once i have time tomorrow

 

So how come when i'm at cruise this was recently when i was doing tutorial 2, i lowered the speed on one of the legs and the aircraft slowed down for that speed i put in? Or does that fit into kriva theory?

Pcubine they engaged last night not sure why they didn't before!

Pcubine they engaged last night not sure why they didn't before!

Vernon

I think you misread the post. I would like to know the origin and destination airports and the runways involved.

EGKK 8R EGPH 24

 

Thanks man

 

 

So how come when i'm at cruise this was recently when i was doing tutorial 2, i lowered the speed on one of the legs and the aircraft slowed down for that speed i put in?

(bold emphasis mine)

As far as I know, you can do pretty much anything within the flight envelope when at cruise. The behaviour I described is only a form of "security" during ascent and descent.