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

Would you abort after V1?

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

Would you abort after V1?

Old 21st May 2008, 00:44
  #201 (permalink)  
 
Join Date: Jan 2008
Location: Blighty (Nth. Downs)
Age: 77
Posts: 2,107
Received 4 Likes on 4 Posts
galaxy flyer:
Yes, V “go” must take Vmcg[1] into account. On 4-engine airplanes configured like the B707, that’s quite limiting to the range of V1s when you are light. But on those (rare) beasts like the VC10, Comet/Nimrod (and maybe Concorde/B1), with less asymmetry, Vmcg can be quite low.
Must admit I’d forgotten the difficulty of obtaining a range of V1s with present-day instant tables or computer programmes. Good idea of yours to use the RTOW case to find the top figure, but wouldn’t know how to find the bottom one. On the VC10, we used to do it all from basic principles, taking about 10 minutes (including a Flex calculation).
Surprised to hear of 50% braking in some single-failure circumstances on your present type.

Pace and Diesel8:
Yes, a double engine failure before VR sounds unlikely on a 3 or 4-eng aeroplane, so why did we consider it unofficially on the VC10? Because the engines are behind the landing gear and mounted in pairs, like the Comet/Nimrod, Jetstar and Concorde (not to mention the B1 and B52). As far as conventional aeroplanes are concerned, there was the El Al B747F that was unlucky enough to throw a blade from one engine into the other over Amsterdam.
By the way, the VC10 can get airborne on 2 quite nicely even at medium-to-high weights, particularly at sea-level. [After all, it’s only like a twin losing one, although the performance regs don’t have to cater for it.] Not so the under-powered Seven-oh. And I seem to remember the 707-320 with JT3D-3Bs had a Vmca[2] of 147kts, so it could not manage it even at low weights, if the failures were on the same side.

ssg:
I know that you are, to some extent, playing Devil’s advocate. But in relation to Flex, don’t forget that TOGA is still available as a bonus (though not assumed in the calculation). De-Rate, of course, is another matter.

Having “taken the shilling”, I advocate sticking to SOPs to the letter; but not all scenarios can have an SOP. The trick that we all hope we will never have to perform is that of recognising that there is no applicable SOP, no time for “DODAR”, and still making a good decision.
Chris Scott is offline  
Old 21st May 2008, 00:49
  #202 (permalink)  
 
Join Date: Dec 1999
Location: Over the horizon
Posts: 230
Likes: 0
Received 0 Likes on 0 Posts
So Chris, in the VC10, if you are at VR and both donkeys on one side decides it is time to eat hay, are you stopping?
Diesel8 is offline  
Old 21st May 2008, 01:04
  #203 (permalink)  
 
Join Date: Dec 2006
Location: The No Transgression Zone
Posts: 2,483
Received 6 Likes on 4 Posts
Chris Scott has written:
Having “taken the shilling”, I advocate sticking to SOPs to the letter; but not all scenarios can have an SOP. The trick that we all hope we will never have to perform is that of recognising that there is no applicable SOP, no time for “DODAR”, and still making a good decision.
Now that is a true/ well conceived / learned and balanced statement--

Ssg you should heed his words brother
Pugilistic Animus is offline  
Old 21st May 2008, 01:07
  #204 (permalink)  
 
Join Date: Dec 2002
Location: Where the Quaboag River flows, USA
Age: 71
Posts: 3,415
Received 3 Likes on 3 Posts
Chris

What I said was that if the engine failure were accompanied by loss of fluid in one of the two systems that power the brakes, I would have 50% of brakes. The brakes on Challenger/Global are divided inboard and outboard powered by system 3 and 2, respectively. Yes, it is a compounding emergency, but loss of fluid quantity could be caused by uncontained hot bits from an engine disintegration. The brakes normally have two pumps powering them-AC and Engine-driven, so it is a remote possibility. Once the fluid is gone, no power for those systems. The C-5 was similar where loss of system fluid required switching to alternate brakes-just a switch actuation by the Co-pilot, but easily missed in the heat of a overspeed abort. But you did then have all the brakes.

My point was it is better to address these issues airborne. I presently have plenty of brakes for stopping with a 50% loss, if it is planned for.

BTW, the C-5 has a low Vmcg of around 80 knots, dry, no crosswind. We computed corrections for both runway condition and crosswind. I'd like to think the low Vmcg was due to having four very powerful APUs as engines.
galaxy flyer is offline  
Old 21st May 2008, 01:10
  #205 (permalink)  
 
Join Date: Dec 1999
Location: Over the horizon
Posts: 230
Likes: 0
Received 0 Likes on 0 Posts
"Now that is a true/ well conceived / learned and balanced statement--"

Agree indeed!
Diesel8 is offline  
Old 21st May 2008, 01:22
  #206 (permalink)  
ssg
Thread Starter
 
Join Date: Dec 2003
Location: USA
Posts: 194
Likes: 0
Received 0 Likes on 0 Posts
Having “taken the shilling”,

Loud and clear...families to feed and all that...a faustian choice....who knows one of these days I might be up there planning my egress into the stop way...rolling down the runway, less power then available, yanking it up at VR, over the fence...rolling left because of the tanker I just clipped...before I go in...I joke to the FO....'well atleast were getting paid'

It's no different then corporate...to be honest...the owners would have me working main st for $5 a pop if they could get away with it...hang on to your unions boys....

P. Animas...don't worry I'm a whore just like everyone else but I have limits...
ssg is offline  
Old 21st May 2008, 01:26
  #207 (permalink)  
 
Join Date: Dec 2006
Location: The No Transgression Zone
Posts: 2,483
Received 6 Likes on 4 Posts
SSG that's the spirit of the business You've been Schooled!!


I'm gonna take my meds now

CAVU!
Pugilistic Animus is offline  
Old 21st May 2008, 02:26
  #208 (permalink)  
ssg
Thread Starter
 
Join Date: Dec 2003
Location: USA
Posts: 194
Likes: 0
Received 0 Likes on 0 Posts
Airlines.....

A jetliner was forced to pull out of a landing at Sao Paulo's Congonhas airport yesterday as new footage emerged of the Airbus 320 that crashed earlier in the week, showing the aircraft travelling along the runway at more than three times the usual landing speed.

Security video footage appeared to show the aircraft hurtling down the runway in just three seconds. Video footage of a similar aircraft landing just minutes beforehand showed the plane taking more than 10 seconds to complete the length of the 1,900m runaway.

More than 180 people were killed when the flight careered off the runway and burst into flames after hitting buildings at the northern end of the airport.
ssg is offline  
Old 21st May 2008, 03:15
  #209 (permalink)  
 
Join Date: Dec 2006
Location: The No Transgression Zone
Posts: 2,483
Received 6 Likes on 4 Posts
BTW, the C-5 has a low Vmcg of around 80 knots, dry, no crosswind. We computed corrections for both runway condition and crosswind. I'd like to think the low Vmcg was due to having four very powerful APUs as engines.
Wow GF---you USAF folks really keet your performance airtight!!!!

and a VMCG of 80 KIAS--or is it KEAS for you?---would never have guessed!
Pugilistic Animus is offline  
Old 21st May 2008, 03:36
  #210 (permalink)  
 
Join Date: Dec 2002
Location: Where the Quaboag River flows, USA
Age: 71
Posts: 3,415
Received 3 Likes on 3 Posts
Mulitple entries in the AF 4098 Take-off worksheet-about 50, I'd guess. A good engineer could do one in 20 minutes, if there wasn't a difficult climb gradient problem. We always had Vmca2, refusal speed on the pilot's card. Normally, refusal and rotate were computed and then compared to Vmbe and Vcefs (critical engine failure) and the limiting one became Vgo (V1). On take-off the PM just called "GO" signally stopping was no longer an option. Did a near GO stop at Sigonella once, just made it. Then "rotate", of course. Gust increment was added to Rotate and V2. It was a very marginally powered aircraft, or too heavy, if you prefer. Above 712,000, its originally gross weight, additions were notable in performance. OEI climb gradient could be as low as 2.3% with no obstacles. Surprising amount of this stuff stuck, but I instructed to pilots. Who were not impressed!

KIAS, not EAS, but Old Smokey smiles at you mentioning it.
galaxy flyer is offline  
Old 21st May 2008, 03:55
  #211 (permalink)  
 
Join Date: Oct 2005
Location: USA
Posts: 3,218
Likes: 0
Received 0 Likes on 0 Posts
KIAS, not EAS,
Oh, heaven forbid...
SNS3Guppy is offline  
Old 21st May 2008, 09:07
  #212 (permalink)  

Mach 3
 
Join Date: Aug 1998
Location: Stratosphere
Posts: 622
Likes: 0
Received 0 Likes on 0 Posts
Diesel8,

I wasn't using those examples as strictly relevant to the case initially proposed in the thread, but rather to demonstrate how what one might consider nigh on impossible, has probably already happened to someone somewhere....

Who would have thought a 777 could have a "double engine failure" on short finals over London until a few months ago (not strictly true, but to all intents and purposes, that is what happened)?

I have to say that everyday I get airborne I'm cognizant of the fact that my flight director scheduling, should I have an engine failure, is designed with AA191's experience in mind. Its a sobering thought.

We all know what the statistics say (although I have to say they won't be much comfort to me when the proverbial hits the fan), we've all read The Pilot Guide to Takeoff Safety...

I'll bow out with a quote from that document:

There is more to the Go/No-Go decision than "Stop prior to V1" and "Go after V1".
Safe flying.

SR71 is offline  
Old 21st May 2008, 10:40
  #213 (permalink)  
 
Join Date: Sep 1999
Location: ME
Posts: 5,502
Likes: 0
Received 0 Likes on 0 Posts
No one said anything about v2 or single engine...Citation Vs, Ultras and Encores can do 4000 ft/m...for while
Actually, if i remember correctly, the statement was from you in repsonse to my question about how you ensured your obstacle clearance during takeoff and climbout.

So now that you are back peddling, please answer the question, how do you ensure your obstacle clearance following an engine failure?

Mutt
mutt is offline  
Old 21st May 2008, 11:07
  #214 (permalink)  
 
Join Date: Jan 2001
Location: In the boot of my car!
Posts: 5,982
Likes: 0
Received 0 Likes on 0 Posts
So now that you are back peddling, please answer the question, how do you ensure your obstacle clearance following an engine failure?

Mutt

A few years ago I was involved with a forum for Microsoft Flight Simulator. I did some development work with addon companies, wrote reviews and was fairly active in their forums.

The problem with all these forums is that they are open to a lot of people who hide behind a cloak and claim to be something they are not.

There was one guy in particular who challenged the real world pilots on those forums and fair enough some of the stuff he came up with was quite convincing.

But in other ways his approach was very purile and he made major blunders.
We discovered that this experienced so called pilot was infact a 12 year old kid who was merrily googling his answers on the internet and somehow getting a kick by playing out his act. He fooled a lot of airline and corporate pilots for some time.

Pace

Last edited by Pace; 21st May 2008 at 14:37.
Pace is offline  
Old 21st May 2008, 14:29
  #215 (permalink)  
 
Join Date: Nov 2001
Location: Somewhere in the Tropics UTC+7 to 9
Posts: 450
Likes: 0
Received 0 Likes on 0 Posts
A jetliner was forced to pull out of a landing at Sao Paulo's Congonhas airport yesterday as new footage emerged of the Airbus 320 that crashed earlier in the week, showing the aircraft travelling along the runway at more than three times the usual landing speed...

This accident was caused by not putting both thrust levers to idle then only reversing the idled engine thus resulting in 1 engine giving positive thrust, the other in reverse, and no spoilers deployed.

It's got nothing to do with aborting past V1... off topic!
What are you trying to pull here? *our legs?*
PK-KAR is offline  
Old 21st May 2008, 16:08
  #216 (permalink)  
 
Join Date: Sep 1999
Location: ME
Posts: 5,502
Likes: 0
Received 0 Likes on 0 Posts
and I am still waiting for those engine overhaul numbers and cost
Do you really think that I'm going to release information that my company considers "commercially sensitive"?

And I dont believe that you did answer the question about obstacles... humor me... quote me the page from the FMS guide where it says that the takeoff path can be calculated with an engine out, and also tell me who is your obstacle data provider......

Mutt
mutt is offline  
Old 21st May 2008, 17:36
  #217 (permalink)  
 
Join Date: Nov 2001
Location: Somewhere in the Tropics UTC+7 to 9
Posts: 450
Likes: 0
Received 0 Likes on 0 Posts
Since SSG is so desperate for the numbers, I'll give him one a from a now defunct operator... got it from the guy who had worked there... accuracy not guaranteed. I can't give the exact numbers for obvious reasons.

Numbers for the 733/4/5, average hour to cycle ratio 1h10m, 10 cycles a day average. Destinations are all <2500m runway (mostly <100ft elev, ISA+15C) except for 5 airports with 3000m - 3600m runways.

Derate take off & derate climb policy = about 50USD per cycle. at 10 cycles a day, equivalent to 100k - 150k USD per year.
Derate take off only would save about 30USD per cycle (less fuel and engine wear, whereas the derated climb expends just a little bit more fuel, but significantly reduces engine wear).
PK-KAR is offline  
Old 21st May 2008, 19:17
  #218 (permalink)  
 
Join Date: May 2008
Location: uk
Age: 68
Posts: 4
Likes: 0
Received 0 Likes on 0 Posts
Curious...what is the cost of the engine they were using and the total cycles allowed...engine cost divided by cycles = cost per cycle.
trickle451 is offline  
Old 21st May 2008, 23:44
  #219 (permalink)  
 
Join Date: Jan 2008
Location: Blighty (Nth. Downs)
Age: 77
Posts: 2,107
Received 4 Likes on 4 Posts
Armchair Decisions

Quote from Diesel 8:
So Chris, in the VC10, if you are at VR and both donkeys on one side decides it is time to eat hay, are you stopping?
[Unquote]

The short (and honest) answer is that I don’t know. The slippery one is that you haven’t supplied me with enough data! [You should ask one of the RAF guys; I’m over 30 years out of date.] Think I should admit first that anything offered here is, by definition, merely an armchair decision...

Let’s assume that ssg’s 5000ft-excess of Balanced Field is leaving us with about 5500ft of runway remaining at Vr.

At sea-level, if not already rotated, I think I’d go, as she should fly okay − even at MTOW. But with that amount of pavement remaining, she should also be able to stop. If rotated significantly, I’d go.

At Nairobi (5327ft amsl, if memory serves), both options are less attractive. TAS/GS would be higher; thrust lower. We’ve already used 8000ft of the 13500ft runway, so we are pretty heavy. Initial climb would be marginal. The gear will have to stay down initially, because of the extra drag of opening the gear doors. Think I’d stop, and almost certainly overrun the runway. If already rotated, I’d have to go, and fuel dumping would start asap.

On the B707-320 with 2 out on the same side, the decision is simple: stop in all cases; because of lack of thrust when heavy, and the high Vmca[2] when light. Cannot comment on the various types of DC-8s, B747s and A340s; never flew them.

Last edited by Chris Scott; 22nd May 2008 at 09:40. Reason: In the comfort and safety of my home.
Chris Scott is offline  
Old 22nd May 2008, 00:01
  #220 (permalink)  
 
Join Date: May 2008
Location: uk
Age: 68
Posts: 4
Likes: 0
Received 0 Likes on 0 Posts
Sounds like one of those..

.'you have to be there..see what the planes actualy doing...make a decision'
trickle451 is offline  

Thread Tools
Search this Thread

Contact Us - Archive - Advertising - Cookie Policy - Privacy Statement - Terms of Service

Copyright © 2024 MH Sub I, LLC dba Internet Brands. All rights reserved. Use of this site indicates your consent to the Terms of Use.