Sponsor Message:
Aviation Technical / Operations Forum
My Starred Topics | Profile | New Topic | Forum Index | Help | Search 
Why Vref+5 On 737? WHat Is It On Your Aircraft?  
User currently offlinesmartt1982 From United Kingdom, joined Nov 2007, 225 posts, RR: 0
Posted (1 year 11 months 1 week 3 days 1 hour ago) and read 6390 times:
Support Airliners.net - become a First Class Member!

Hi,

In the FCTM for the 737 it states that the minimum command speed setting is VREF + 5 knots. Why is this? I have been told that we should bleed these 5 knots off over the threshold because your landing distance is based on touching down at VREF?

Is this the same for all Boeings/other aircraft makes, I have heard other aircraft like the BAE 146 approach @ VREF and downtown at less than VREF

9 replies: All unread, jump to last
 
User currently offlineKAUSpilot From United States of America, joined Jan 2002, 1958 posts, RR: 33
Reply 1, posted (1 year 11 months 1 week 3 days 1 hour ago) and read 6373 times:

It's the same in both the EMB-145 and B744. Why? The airplanes were designed to fly the final approach at that speed. Through the course of a normal flare maneuver the 5 knots will usually be bled off just as the aircraft touches down. Flying for extended periods at Vref puts you too close to stick shaker in my opinion. Of course there are also additives for strong winds.

User currently offlinederekf From United Kingdom, joined Feb 2001, 888 posts, RR: 0
Reply 2, posted (1 year 11 months 1 week 2 days 22 hours ago) and read 6308 times:

The BAe146 flies approach at VREF+5 and should touch down at VREF-7.


Whatever.......
User currently offlinetdscanuck From Canada, joined Jan 2006, 12709 posts, RR: 80
Reply 3, posted (1 year 11 months 1 week 2 days 22 hours ago) and read 6295 times:

Quoting smartt1982 (Thread starter):
In the FCTM for the 737 it states that the minimum command speed setting is VREF + 5 knots. Why is this?

Because the autorthrottle certified +/- 5 knots. It's the only way to have the authothrottle and the landing certification standards "get along" (the autothrottle can't put you below Vref).

Quoting smartt1982 (Thread starter):
I have been told that we should bleed these 5 knots off over the threshold because your landing distance is based on touching down at VREF?

You can, you don't have to. The flare will naturally shed speed and the throttles should be at idle at that point.

Quoting smartt1982 (Thread starter):
Is this the same for all Boeings/other aircraft makes

It's the same for all Puget Sound heritage Boeing's, I'm not sure about the others.

Tom.


User currently offlineBA777 From United Kingdom, joined Jun 2001, 2167 posts, RR: 7
Reply 4, posted (1 year 11 months 1 week 2 days 1 hour ago) and read 5970 times:

We have a correction for every 5 knots over VREF so add that to our landing distance calculations

User currently offlinesmartt1982 From United Kingdom, joined Nov 2007, 225 posts, RR: 0
Reply 5, posted (1 year 11 months 6 days 2 hours ago) and read 5573 times:
Support Airliners.net - become a First Class Member!

Quoting tdscanuck (Reply 3):
Because the autorthrottle certified +/- 5 knots. It's the only way to have the authothrottle and the landing certification standards "get along" (the autothrottle can't put you below Vref).

so because the autothrottle is +/- 5 knots you have to always set +5 so the autothrottle will never go below vref?


User currently offlinetdscanuck From Canada, joined Jan 2006, 12709 posts, RR: 80
Reply 6, posted (1 year 11 months 6 days 2 hours ago) and read 5565 times:

Quoting smartt1982 (Reply 5):
so because the autothrottle is +/- 5 knots you have to always set +5 so the autothrottle will never go below vref?

That's basically it, yes. It's more complex in the details (it always is) but that's the meat of it.

Vref is somewhat arbitrary...an alternative method would be to just bump Vref by 5 knots and not do the +5 increment but that would break a ton of commonality requirements.

Tom.


User currently offlinesmartt1982 From United Kingdom, joined Nov 2007, 225 posts, RR: 0
Reply 7, posted (1 year 11 months 6 days 2 hours ago) and read 5560 times:
Support Airliners.net - become a First Class Member!

Thanks Tom.

Where could one find out more detail behind it?

Cheers
Steve


User currently offlinetdscanuck From Canada, joined Jan 2006, 12709 posts, RR: 80
Reply 8, posted (1 year 11 months 5 days 7 hours ago) and read 5413 times:

Quoting smartt1982 (Reply 7):
Where could one find out more detail behind it?

A Boeing training pilot would be a good place, if you've got access to one (that's where I got my information). The Boeing Flight Crew Training Manual (737NG) says, for a stabilized approach, "the airplane should be at approach speed. Deviations of +10 knots to – 5 knots are acceptable if the airspeed is trending toward approach speed". Note that, coupled with Vref+5 approach speed, means that following standard procedure should keep you at or above Vref.

The speed portion of the FCTM also says, "When using the autothrottle, position command speed to VREF + 5 knots.
Sufficient wind and gust protection is available with the autothrottle connected because the autothrottle is designed to adjust thrust rapidly when the airspeed drops below command speed while reducing thrust slowly when the airspeed
exceeds command speed." That's basically a tacit admission that the autothrottle will hold you to at least VREF when you set commanded speed to VREF+5.

A different portion says, "When using the autothrottle, position command speed to VREF + 5 knots. Sufficient wind and gust protection is available with the autothrottle engaged that no further wind additives are needed."

Tom.


User currently offlineCosmicCruiser From United States of America, joined Feb 2005, 2254 posts, RR: 16
Reply 9, posted (1 year 11 months 5 days 7 hours ago) and read 5400 times:

We do ref+5 regardless of A/T or not. The FMS defaults to it. EO is ref +10. we ad the wind factor regardless of direction, head, tail, x-wind. I was just thinking it was a "safety pad" so you wouldn't go below ref (1.3 stall) especially at heavy ldg wgts.

Top Of Page
Forum Index

Reply To This Topic Why Vref+5 On 737? WHat Is It On Your Aircraft?
Username:
No username? Sign up now!
Password: 


Forgot Password? Be reminded.
Remember me on this computer (uses cookies)
  • Tech/Ops related posts only!
  • Not Tech/Ops related? Use the other forums
  • No adverts of any kind. This includes web pages.
  • No hostile language or criticizing of others.
  • Do not post copyright protected material.
  • Use relevant and describing topics.
  • Check if your post already been discussed.
  • Check your spelling!
  • DETAILED RULES
Add Images Add SmiliesPosting Help

Please check your spelling (press "Check Spelling" above)


Similar topics:More similar topics...
What Is On The Ceiling Here? posted Mon Nov 26 2007 15:46:48 by BR715-A1-30
"Finger Tapping" Sound On MD-88-What Is It? posted Sat Feb 4 2006 02:38:46 by DeltaGator
"Licensed Aircraft Engineer", What Is It Exactly? posted Fri Aug 5 2005 01:33:35 by Sabena332
Loud Sound:What Is It? posted Tue Apr 26 2011 10:48:36 by Chamonix
NDT, What Is It? posted Sat Aug 9 2008 07:11:09 by AcNDTTech
What Is Wrong With This Aircraft's APU? posted Sat Dec 29 2007 00:18:50 by DIJKKIJK
Engine Testing And Sphere What Is It? (Video) posted Mon Feb 26 2007 15:42:44 by Airfoilsguy
What Is This Around The Aircraft? posted Thu Feb 15 2007 02:44:25 by LoveASE
What Is The Best Corporate Aircraft Forum? posted Sat Jan 6 2007 05:56:01 by Turbonytro
'Triller' ... What Is It Used For? posted Thu Dec 28 2006 01:51:53 by Tom12
What Is On The Ceiling Here? posted Mon Nov 26 2007 15:46:48 by BR715-A1-30
"Finger Tapping" Sound On MD-88-What Is It? posted Sat Feb 4 2006 02:38:46 by DeltaGator
"Licensed Aircraft Engineer", What Is It Exactly? posted Fri Aug 5 2005 01:33:35 by Sabena332
Loud Sound:What Is It? posted Tue Apr 26 2011 10:48:36 by Chamonix
NDT, What Is It? posted Sat Aug 9 2008 07:11:09 by AcNDTTech
What Is Wrong With This Aircraft's APU? posted Sat Dec 29 2007 00:18:50 by DIJKKIJK
Engine Testing And Sphere What Is It? (Video) posted Mon Feb 26 2007 15:42:44 by Airfoilsguy
What Is This Around The Aircraft? posted Thu Feb 15 2007 02:44:25 by LoveASE
What Is The Best Corporate Aircraft Forum? posted Sat Jan 6 2007 05:56:01 by Turbonytro
What Is On The Ceiling Here? posted Mon Nov 26 2007 15:46:48 by BR715-A1-30
"Finger Tapping" Sound On MD-88-What Is It? posted Sat Feb 4 2006 02:38:46 by DeltaGator
"Licensed Aircraft Engineer", What Is It Exactly? posted Fri Aug 5 2005 01:33:35 by Sabena332
Loud Sound:What Is It? posted Tue Apr 26 2011 10:48:36 by Chamonix
NDT, What Is It? posted Sat Aug 9 2008 07:11:09 by AcNDTTech
What Is Wrong With This Aircraft's APU? posted Sat Dec 29 2007 00:18:50 by DIJKKIJK
Engine Testing And Sphere What Is It? (Video) posted Mon Feb 26 2007 15:42:44 by Airfoilsguy
What Is This Around The Aircraft? posted Thu Feb 15 2007 02:44:25 by LoveASE
What Is The Best Corporate Aircraft Forum? posted Sat Jan 6 2007 05:56:01 by Turbonytro
Engine Testing And Sphere What Is It? (Video) posted Mon Feb 26 2007 15:42:44 by Airfoilsguy
What Is This Around The Aircraft? posted Thu Feb 15 2007 02:44:25 by LoveASE
What Is The Best Corporate Aircraft Forum? posted Sat Jan 6 2007 05:56:01 by Turbonytro

Sponsor Message:
Printer friendly format