Go Back  PPRuNe Forums > Flight Deck Forums > Tech Log
Reload this Page >

More unheard of ideas: NG speed restriction

Tech Log The very best in practical technical discussion on the web

More unheard of ideas: NG speed restriction

Old 3rd Jul 2016, 10:59
  #41 (permalink)  
 
Join Date: Sep 2008
Location: 41S174E
Age: 52
Posts: 2,767
I'm with you VA. My experience is that about once a year it pays off.
framer is offline  
Old 4th Jul 2016, 04:12
  #42 (permalink)  
 
Join Date: Aug 2013
Location: PA
Age: 54
Posts: 35
I can see three different possibilities Underfire;
1/ you were in a rush and what you wrote above was in error.
2/ you operate FMC updates that are fundamentally different to any I have seen since 10.4
3/ You really shouldn't be validating RNP procedures for any passenger carrying airline until you understand the basics.
Which one do you reckon?
Nice reply, I expected no less from you. We have to design procedures with the lowest common denominator in mind. There are ac running these configurations. (as noted by the FCOM screenshots)

There are plenty of other posts referencing the 240kts as the default on Boeing ac. Most pilots also rumble that it is to prevent a bust below 10K.

What is your take?
underfire is offline  
Old 4th Jul 2016, 05:13
  #43 (permalink)  
 
Join Date: Jun 2006
Location: Brisbane
Posts: 907
This thread should be deleted, quickly, before anyone else reads it.
Derfred is offline  
Old 4th Jul 2016, 08:00
  #44 (permalink)  
 
Join Date: Sep 2008
Location: 41S174E
Age: 52
Posts: 2,767
Nice reply, I expected no less from you.
Yip that's a fair call. I wouldn't have said that to your face so I shouldn't have said it here. I apologise.
I don't think anyone is disputing that the system defaults to 240kts. Certainly not me.
the system defaults to 240kts below 10K in VNAV. If you bust 250kts below 10K, it will go to LVL CHG
The above statement is incorrect. The only time it will go to LVL CHG is if you get very slow, pretty much the opposite of the scenario you describe. It is possible that there are FMC logic variations floating about that I have not come across, if that is the case I'm standing by to learn something.
Again, apologies for being a rude grumpy pr1ck.
framer is offline  
Old 4th Jul 2016, 17:04
  #45 (permalink)  
 
Join Date: Jan 2007
Location: EU
Posts: 1,218
This thread should be deleted, quickly, before anyone else reads it.
Sorry to sound naiive, but why?

Seems like a pretty lively discussion, some of which may have missed the point of the original query but garnered a bit of interest.
Mikehotel152 is offline  
Old 5th Jul 2016, 10:35
  #46 (permalink)  
 
Join Date: Aug 2013
Location: PA
Age: 54
Posts: 35
framer, no worries.

According to what I understand, VNAV will revert to LVL CHG to prevent overspeed. As you state, there are many possible combinations and options to consider. That is why I enjoy these conversations, and there are many combinations that are difficult to consider. Field operations, has exposed many, many issues.

As you stated VNAV will disco to LVL CHG if the ac goes below min speed, but my understanding is that VNAV will disco if you go overspeed with gusts (hence the 240) It also may disco to VNAV SPD on overspeed. In reality, I am unclear as to gust overspeed vs overspeed, based on what I have experienced.

Perhaps this is where the confusion comes in, at least on my part, but, what I do know is that it is a problem (or at least was) when you code a waypoint at 10K with a speed restriction of 250kts on the B models. Airports and the advance of procedure design,...the coding itself has introduced anomalies that had never occurred before, such as a RWY point over 10K, the box just could not do it. (the damn 10K is hard coded and buried in the code of so many areas...)

Regards

Last edited by underfire; 5th Jul 2016 at 10:59.
underfire is offline  
Old 5th Jul 2016, 10:55
  #47 (permalink)  
 
Join Date: Aug 2013
Location: PA
Age: 54
Posts: 35
The Vmo of the 737NG "here" below 10k is 340, as it is with my "little Boeing".
just curious, looking at the CASA regs:




just how much of the airspace below 10K can you drive over 250 kts?
underfire is offline  
Old 5th Jul 2016, 12:19
  #48 (permalink)  
 
Join Date: Mar 2002
Location: Seat 0A
Posts: 7,795
It's the regs, underfire.
Capn Bloggs is offline  
Old 5th Jul 2016, 16:17
  #49 (permalink)  
 
Join Date: Jan 2006
Location: US
Posts: 2,070
Underfire - class E, first line, ends with an *. What does the statement next to the * say?
That's usually where the exception is made where 250 below 10,000 is approved.
misd-agin is offline  
Old 5th Jul 2016, 17:24
  #50 (permalink)  
 
Join Date: Mar 2001
Location: I wouldn't know.
Posts: 3,956
Apparently Class C for IFR traffic. That seems to cover control zones and the associated steps leading to that airport.

Anyway, it seems kinda similar to how it is over here in germany, below 100 it is allowed in Class C and whenever approved by an ATCO in protected airspace (Class D not Control Zone for example). But companies can have stricter limits, mine for example has a non type dependent general speed limit of 250kias below FL100 except if a specific higher speed is asked for by ATC (high speed approved is not enough), however 250kias is an absolute limit 5000ft and below.
Denti is offline  
Old 5th Jul 2016, 20:34
  #51 (permalink)  
 
Join Date: Jun 2000
Location: last time I looked I was still here.
Posts: 4,510
But we are back to the basic question: not of if it's allowed by the regs, and often it is not, or SOP's, but does it make good airmanship common sense in most cases? You CAN do lots of things, but is it necessarily a good idea.
RAT 5 is offline  
Old 6th Jul 2016, 08:33
  #52 (permalink)  
 
Join Date: Jul 2001
Location: Australia
Posts: 4,942
Folks,
Re. the FMC default 240/10,000.
The US speed limit is MAX 250 below 10,000, there is no +/- 10, or any other tolerance that is applicable in many jurisdictions, this point has "sort of " been made.
The US speed limit is a statutory limit, FAA ATC have no authority to give you a waiver, but there is the authority of the PIC under the rule FAR 91.117(d).
Tootle pip!!
PS: Don't pick me up on some of the trials of greater than 250 below 10, they were approvals by the Administrator per. FAR 91.117(a), not ATC.
LeadSled is offline  
Old 6th Jul 2016, 12:01
  #53 (permalink)  
 
Join Date: Jan 2000
Location: FL410
Posts: 839
FMC defaults to 240/FL100 for ONE reason: VNAV will NEVER exceed 250kts below FL100!
VNAV allows for +10kts faster to be flown, thus defaulting to 240 ensures compliance.
Conversely, the A/T "wakes up" when VNAV gets -15kts below commanded VNAV speed.
Use the systems as they are designed, in parallel, and we end up with an aircraft idle descent not exceeding limitation...

Regarding CI, as mentioned in this post:
1) CI for descent is linear between KIAS and CI, hence low CI relates to low KIAS, 6 being 245, 0 being optimum glide for fuel at 239.
2) CI for CRZ and CLIMB take into account many more parameters such as weight, level, toc wind (calculating a speed correction for the calculated hw/tw component 150nm along the track direction after takeoff by using the angular difference between the track and toc wind direction), toc isa, to name a few...
Skyjob is offline  
Old 6th Jul 2016, 16:39
  #54 (permalink)  
 
Join Date: Jan 2006
Location: US
Posts: 2,070
Rat5 - But we are back to the basic question: not of if it's allowed by the regs, and often it is not, or SOP's, but does it make good airmanship common sense in most cases? You CAN do lots of things, but is it necessarily a good idea.


Except for the USA it's typically allowed by the regs and individual companies have different SOP's, as Denti mentioned. So if the regs allow it, and the SOP's allow it, the common sense question is an opinion not supported by the regs or SOP's.

The answer to the question 'is it good airmanship in most cases' is yes, provided there aren't other reasons not too. Like specific arrivals that have known bird issues or during bird migratory seasons.
misd-agin is offline  

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are Off
Refbacks are Off


Thread Tools
Search this Thread

Contact Us Archive Advertising Cookie Policy Privacy Statement Terms of Service

Copyright 2018 MH Sub I, LLC dba Internet Brands. All rights reserved. Use of this site indicates your consent to the Terms of Use.