Speed limit not taken into account

[falcon71]

Hello, I flew the approach DNMM ILS 21 EREK1B. I modified the DES SPD LIM (LSK 4R) in the VERT REV page:

On the FPLN page it still showed a reduction to 250 knots below FL100 and PROFILE mode still slowed down to 250 knots at FL100. I would have expected the aircraft to remain at 285 knots.

Also, when I cleared the limit, it switched to the above displayed 285/FL100. The FCOM makes it sound like it should revert to the default (250/10000). I'm not sure though if this behavior is dependent on the FMC software version, but it might be worth to check.

[Crabby]

EREKA does not have an altitude or speed constraint on the chart.  The first constraint is ASGAR at FL090.  Most of the time you would want to be at 10k (or FL100) within 30 nm of your destination.  EREKA is a bit over 40 nm.  It looks like the FL100 is being predicted (the asterisk).  I will have to check the FCOM, but the normal indications there are, for example, 5000 for AT that altitude, +5000 for at or above, and -5000 for at or below.  So, I believe that altitude is predicted. However, you would have been close to FL100 at that point and the aircraft would possibly be beginning its speed reduction to 250 and it takes a while to do so. 

[falcon71]

Hi Crabby,

I was not talking about the altitude restrictions, those worked pretty well actually. I was talking about the speed limit (not the speed restriction either!). As you can see, the speed limit was changed to 285/FL100. The aircraft should not have slowed down to 250 knots below FL100.

[Crabby]

12 minutes ago, falcon71 said:

Hi Crabby,

I was not talking about the altitude restrictions, those worked pretty well actually. I was talking about the speed limit (not the speed restriction either!). As you can see, the speed limit was changed to 285/FL100. The aircraft should not have slowed down to 250 knots below FL100.

Yes, however the DEFAULT speed limit at/below 10K(FL100) is 250 and it should absolutely slow down unless you changed the default. Did you change it to 285?  That could be the reason for the asterisk.  

[falcon71]

Well, I think I did. It looks like my screenshot above. Is there anything else I needed to do to change the speed limit?

[Crabby]

32 minutes ago, falcon71 said:

Well, I think I did. It looks like my screenshot above. Is there anything else I needed to do to change the speed limit?

I am not sure where it is at in the FMC and I am not in the plane at this time.  

I guess I also wonder why you would want to change the speed at that altitude/flight level as there is an actual speed limit there.  Granted we are in a sim, but most folks want to fly realistically and in real life you cannot go 285 at that altitude.  

[falcon71]

I'm sorry. I just noticed, I wrote DNMM in the initial post. The STAR and Approach actually belong to DGAA, but I think you already figured that out.

DGAA does not have any speed limits, this can be verified in the regulations (specifically part 19 and part 24):
https://www.gcaa.com.gh/web/?p=651

 

[Crabby]

8 hours ago, falcon71 said:

I'm sorry. I just noticed, I wrote DNMM in the initial post. The STAR and Approach actually belong to DGAA, but I think you already figured that out.

DGAA does not have any speed limits, this can be verified in the regulations (specifically part 19 and part 24):
https://www.gcaa.com.gh/web/?p=651

 

Ok, the plane defaults to 250 at and under 10K.  

As far as Ghana, they are a council member of ICAO.  ICAO specifically states that operations at/below 10K are restricted to 250.  Ghana's own regulations call out the penalty/suspension for exceeding speed limits in "critical phase of flight".  They define critical phase of flight as below 10000.  I have seen reference to China not having this limit and they too are council members of ICAO so there is that.  Apparently, they never adopted ICAO airspace classification with the exception of Sanya Oceanic space where they use feet and there is the ICAO/FAA restriction.  

However, mention was made that most pilots flying into and out of China are flying Boeing and Airbus so having the restriction as "law" does not matter as those aircraft are speed restricted by default.  On Boeing you can change it (not sure if higher or not would have to look) and on Airbus there does not appear to be a way to change it.  At the end of the day the restriction is to make it easier to see traffic and other hazards like birds.  I would not see a need to exceed that speed giving the proximity to the arrical airport when reaching 10K. 

[falcon71]

2 hours ago, Crabby said:

As far as Ghana, they are a council member of ICAO.  ICAO specifically states that operations at/below 10K are restricted to 250.  Ghana's own regulations call out the penalty/suspension for exceeding speed limits in "critical phase of flight".  They define critical phase of flight as below 10000.  I have seen reference to China not having this limit and they too are council members of ICAO so there is that.  Apparently, they never adopted ICAO airspace classification with the exception of Sanya Oceanic space where they use feet and there is the ICAO/FAA restriction.  

 

You refer to ICAO Annex 11. They provide this handy chart:

Now, most countries obviously do have their own regulations in place to enforce speed limits. However, I did not find any such regulations for Ghana or the approach into Accra and since the STAR into DGAA is entirely within class A and B, I have to assume, that there is no speed limit in place. 

In Boeing aircraft, you can delete the speed limit in the climb and descend pages. This also applies to the MD-80. In the A320 the speed limit can be modified and cleared on the VERT REF page of the (LIM) waypoint. I do however agree with you that higher speeds below FL100 carry additional risks.

[Crabby]

Class A airspace is from FL180 to FL600, so that does not matter.  Class B airspace is generally 0 feet to 10000 feet msl, therefore you should be at or under 250 there anyhow.  Most Class B has a speed restriction of 200 knots.  This is why the speed limit is not applicable.  In essence, no matter what Class B you are in you will already be below 250 knots if you are legal.  

Yes, you can delete the speed limits in some aircraft, however that is like my truck.  It can do well over 100 mph (Go 5.7 L Hemi!), but I will hit the speed limit before I hit the engine limit.  I will guarantee you that if you go screaming into DGAA below 10K at 285 you will end up with several numbers to call at a minimum.  

[falcon71]

You are talking about the CFR:

https://www.ecfr.gov/current/title-14/section-91.117

Those apply to the United States only. Have you found any such laws regarding aircraft speed limits for Ghana?

[Crabby]

I am not talking about the CFR.  I am talking about ICAO airspace classifications and speed restrictions.  You are interpreting things incorrectly.  

 

[falcon71]

And I have shown you ICAO Annex 11 before:

We are talking in circles.

[Crabby]

LOL, not applicable does not mean no limit exists.  If you are in Class B air space you are on final or taking off.  You are NOT interpreting the information you are presenting correctly.  Good luck to you. 

[falcon71]

All right Crabby, let's blow your mind. That's what people have to say about Europe:

https://aviation.stackexchange.com/questions/1294/what-is-the-speed-limit-in-european-airspace

Again, that's the theory. In practice you will find regulations, publications, procedures and at the very least ATC that will limit your speed in Europe. I really tried to find anything for Ghana. If you have found anything for Ghana, then please share. But you can't just throw out random claims with no backing sources. Let's keep it factual please.

[falcon71]

To get back on topic: I flew to nearby DNMM today (arrival was BUDS1N). They have a speed limit of 230 knots below FL100:

The aircraft still decelerated only to 250 knots, busting the speed limit. It appears to me, that the 250 knots are hardcoded in the iniBuilds version, not taking the value from the VERT REV page into account at all.

[Deleted Account]

Thanks, we will take a look 🙂