Reduced V1 on Dry Runway - (previously) Is V1min a Safety Benefit

[Jambo Buana]

Flying with an American Airlines Direct entry Captain a few weeks ago. He mentioned that they by way of SOP, AA always reduced V1 to its minimum value.
Given that 2/3 of runway overrun incidents were unnecessarily rejected in the first place is this a good policy and how many of the EU operators out there follow this policy?
Thanks

[rhovsquared]

http://www.pprune.org/forums/showthread.php?t=208658 this thread covers this topic and V1 in general

[Jambo Buana]

Thanks Rho, but my question is, does any EU airline drop V1 to its minimum value, ie VMCG plus 1kt when possible? This is what AA do, allegedly! From the post you sent me to, it appears many are unaware that there is often a range of V1s for a given runway. It appears that AA use this range by selecting the min V1 possible. So is it true that AA does this and does anyone else in Europe?

I really dont want to go over the theories of perf all over again and individual "test" pilots theories on calling it early etc etc.

Does your airline drop V1 to its min value?

[BOAC]

Not one of the three UK airlines I have worked for do, and this is the CAA's advice on it.


"Some margins are provided in the continued take-off performance in the event of a decision to continue the take-off with an engine failure below V1
but these could be eroded to such an extent that the aeroplane may not be able to lift off by the end of the runway and/or to clear obstacles once airborne. This is particularly so when using a 'wet' V1. 'Wet' V1 accounts for the reduced stopping capability on a wet runway, but it also reduces the margins in the continued take-off performance compared to the dry runway situation."


I would suggest that you would have to have full performance factors for the runway/obstacles to start messing with V1 for no particular reason. If the runway is so long that V1 can safely be reduced and still enable a 'go' then stopping at V1 is equally not a problem? There are places like JER27 and FNC where it might be a good idea.

[rhovsquared]

Jambo buana I'm not an airline pilot just a pilot CPL-IR ASEL/AMEL who loves jets can't afford more time in anything (not even a passenger ticket on jetblu:O ) otherwise i'd be typed on all of the Boeings:8 ; but my knowledge of the subject is not superficial. Without plaigerizing others here i'm under the impression ( either old smokey or john tullamarine IIRC...sorry guys) that V1/VR/V2 triplets cannot/ or shouldn't be fooled around with on a mix and match basis, so normally V1 should not be tampered with unless the AFM allows a V1 range either V1 min. For field length limitations (such as when a clearway exist that can be overflown within the TODA and the aircraft meets appropriate screen heights for rwy conditions -ASDA v. ASDR- and obstacle clearance on the first and second segments of the net flight path. and everything is scheduled in the perf. tables or afm or the perf pages of the afm or the FMC. and nothing is overtly limiting ). or pick a V1 max for wat limited or obstacle limited departures where you want to stop as late as possible where field length is obviously not limiting and AOTA)) and as you said V1 can never be less than Vmcg cuz you'd drift of the side at high power. now as far as EU, well I have enough trouble with some of the FARs US gov't speak:yuk: so i definitely can't help with the BCARS:\ . but if you look through that thread I know a discusion of V1 min is therein (I know it's quite a long one took me two days to finish). it seems that V1 is quite a contentious issue at times, but just remember the Vmcg and Vmca and Vxse etc. for pistion twins:eek: and playing with the SE GA's such a huge pucker factor that the FAA doesn't even put in the ME PTS's. I'd rather have V1/VR and V2 than Vmc, Vxse, Vyse and a "real" (not on seminoles) critical engine that in XW's is even more critical... in a way life's a bit easier when you're over 12500 lbs MGTOW:D

edited to add a small digression and to correct some grammar and spelling

[TomConard]

My old company in the U.S., after a 737-400 accident at LaGuardia, adopted Boeing's suggestion that V1 could be 'reduced' as conditons permit...as conditions warrant. This does not necessarily mean that the 'MIN V1' is VMGC +1 or whatever. But, it's a perfomance issue that considers takeoff flap settings, density altitude, derated engines (or not), close-in obstacle conditions (first segment climb requirements), runway length, runway conditions, etc., etc.

Boeing (and Airbus, I'm sure) has charts and graphs for just about any combination of conditions and situations. What my old company did was absolutely in accordance with the AFM...totally Boeing approved (and Boeing suggested)...totally FAA approved...and, when applied prudently, added to the safety margin for takeoffs.

Additionally, the 'final numbers' that were computer generated gave a normal V1, and a minimum V1. (Again, Min V1 was not necessarily VMGC limited...and in most cases it was well above VMGC.) It was the captain's decision. He/she could use the normal V1, the minimum V1 or any number in between.

The restrictions were: (1) Whatever V1 was chosen, it was a for real V1...once decided, it was carved in stone, (2) It had to be briefed what this V1 speed was...and, as well, what Vr was...and, as well, not to rotate prior to Vr (but to rotate at Vr).

Again, the computer-generated speeds were all AFM, Boeing, FAA, and company approved. And, it worked very nicely. Coming out of La Guardia on a snowy day reduced the pucker factor just a bit, knowing that with the reduced V1, you at least had some chance of stopping (assuming you rejected properly, etc.) prior to the end of the runway.

Tom

[mutt]

Again, the computer-generated speeds were all AFM, Boeing, FAA, and company approved. And, it worked very nicely. Coming out of La Guardia on a snowy day reduced the pucker factor just a bit, knowing that with the reduced V1, you at least had some chance of stopping (assuming you rejected properly, etc.) prior to the end of the runway.

Tom, the computer generated speeds are approved, however, i think that you will find that contaminated runway v-speeds were "ädvisory" information only and arent in the FAA AFM.

Mutt

[john_tullamarine]

There are various ways to skin a cat with respect to V1.

However, consider the following as being a reasonable approach ..

(a) presuming that you have an RTOW table for the specific runway (this gives you a schedule of RTOW/V1/VR/V2 against wind and OAT

(b) if you select the actual TOW then you will get the airline's required data being the lower speed boundary (presuming that the actual TOW is not limiting)

(c) if you go to the actual OAT you will get the upper speed boundary for the limiting RTOW

(d) dependent on airline SOP policy, there is nothing to prevent your using any scheduled data within the OAT range bounded by (b) and (c)

(e) not a good idea to mix and match schedules, though .. ie one should not use the lowest V1 (b) with the highest VR/V2 (c). Rather you pick a set of V1/VR/V2 as published in the table.

(f) the story can be complicated a tad more if you wish to include reduced thrust procedures but the principles remain the same.

In general you will be nowhere near Vmcg .. this generally only is a problem for very light weights .. however, be aware of the real world effect of crosswind on "actual", as opposed to certification (AFM), Vmcg.

So far as the pilot's picking an attractive V1 to suit the occasion based on nothing much more than "it seemed to be a good idea" .. can't really support that sort of approach to the problem ..

As for me, if the actual weight data does not give an accel-stop limiting (or near limiting) takeoff .. I'd just go with the scheduled data ..

[O\ZON]

Probably 90% of Airbus (fly-by-wire) operators using standard RTOW charts use V1 min.
Indeed, its a requirement in FCOM II, that if you are to use the corrections for wet or contaminated runways, your RTOW chart must be based on V1 min.


O/z

[TomConard]

Again, the speeds are Boeing, Boeing's AFM, and FAA approved. They have to be, in order to satisfy performance standards.

Essentially, when these speeds come into play is when the accelerate/stop is more restrictive than the accelerate/go. By reducing the V1, the two come close to being in balance.

Again, this was the SOP at my old airline. Nothing 'advisory' about it. It was SOP. Boeing gave their blessing (along with the performance figures), and FAA gave their explicit approval.

Tom

[mutt]

Tom, would you be so kind as to quote the appropriate FAR25/121 reference for this AFM data? Alternatively, could you please give me a page reference in the AFM.

As an FAA certified operator of 17 different versions of Boeing airliners certified under FAR25, I have NEVER seen contaminated runway correction data in any FAA Approved Airplane Flight Manual. I'm therefore surprised that they granted approval to 1 specific airline.

We base our contaminated runway information on FAA AC91-6B and the data provided in the Operations Manual.

Mutt

[TomConard]

Mutt,

Honestly, I cannot quote anything!!! :> :> :> :>

But, I can tell you, definitively, that the reduced V1 is the SOP of my old carrier. And, with wet or contamiated runways, the figure routinely came across with the weight and balance figures from the ACARS uplink.

It was very nice to have. For example, you're doing a runway 01 takeoff in DCA...it's been snowing...runway is in good shape, though (relatively)...and the numbers come up on the ACARS.

Min V1 V1 Vr V2
128 141 143 148

(I'm just making these numbers up...)

But, the captain has the authority to choose his V1 anywhere between 128 and 141 (inclusive). Again, the only restriction in the SOP stated that, once the V1 is chosen, it is to be flown.

So, if, in the above example, the guys decide that 135 would be a prudent figure for V1, and an engine fails at 136, a "GO" is absolutely mandatory.

The other caveat as explicitly stated in the manual is that the V1 - Vr spread is emphasized. (Yes, my old carrier had another accident in LaGuardia, partially because the captain rotated early, rotated aggessively, with contaminated wings. There was a sizable spread between V1 and Vr.) So, this spread, under their SOP, must be briefed.

Incidently, a related SOP, the V1 call by the PM (Pilot Monitoring a.k.a. PNF :> :> :>), is made 5 knots prior to V1. So, in the above example, even if the guys were to choose the absolute minimum V1 of 128, the V1 call during the takeoff roll would occur at 123. Of course, once the call is made...you 'go'.

I can tell you, most definitely, that Boeing professes these procedures. They explicitly stated all of this at a special safety symposium they held for my old company...after the series of accidents. (I was there, took notes, and remember all of this....despite my failing memory. :> :>:>) Present in the hotel ballroom was FAA, both from the Air Carrier District Office, and from Washington. Six months after this meeting, the above-stated procedures became the airline's SOP.

Another interesting bit I got out of this meeting is the fact that Boeing has a bazillion graphs/charts, etc. with regard to aircraft performance. They're all "FAA Approved". What we, as pilots see in our manuals, is just a small sample of what Boeing has...really not much more than the minimum what the FAA requires.

For example, before this seminar, I never knew that Flaps 25 was 'an approved' takeoff flap setting on the 737. I've never seen numbers for a Flaps 25 takeoff...I've never heard of anyone using Flaps 25 for takeoff...but, the numbers exist, the performance (under certain contitions) meets FAA requirements, and it's FAA approved. The point, there are a lot of things regarding aircraft certification/performance, etc., that we, as pilots, never heard of (and may think are weird as heck)...but they're there, they're FAA approved, and they can be used (as part of the airline's SOP, of course).

Thanks for the opportunity to chat with you about this. I find all this stuff interesting, although I don't know nearly enough about it as I should.


Tom

[ferrydude]

Perhaps not in the AFM, but most certainly in use with certificated operators and approved by both Boeing and the Feds.
http://www.airweb.faa.gov/Regulatory_and_Guidance_Library/rgAdvisoryCircular.nsf/0/fbffc4ad745e844b862569ea006960d0/$FILE/ATTPCMY6/AC120-62.pdf
http://www.boeing.com/commercial/aeromagazine/aero_11/takeoff_story.html#approved

[TomConard]

Ferrydude,

Thanks for the link that further explains the V1 concept. After reading this, I remember another enlightening tidbit that was discussed at this seminar.

V1...the definition thereof...is quite different from what I was taught. Boeing claims the FAA's classic definition is incorrect from the start...and that aircraft certified in the U.S. under FAR Part 25 were never certified under the classic definition (i.e. decision speed).

Instead, Boeing (as described in this seminar that was held for us in the early nineties) maintains that, from an engineering standpoint, the V1 is the maximum speed the aircraft can attain (thus, the maximum kinetic energy) and still be able to stop on the remaining runway.

In other words, the design braking capability of the aircraft is capable of dissipating only so much kinetic energy (for a set of given conditons)...and at V1 (for that set of given conditions), the brakes need "X" amount of runway distance to dissipate that amount of kinetic energy. On a takeoff where you're accelerate/stop limited, the amount of runway you have remaining exactly at the point V1 is reached...is the exact amount the braking system needs to dissipate that much kinetic energy.

To put it simply, if V1 is, say for example 135, and assuming the takeoff is field-length limited for accelerate stop, then rejecting the takeoff at 136 will cause an overrun. The braking capability is insufficient to dissipate that much kinetic energy in the runway distance remaining.

Or, to put it another way...135 is the "brakes on" speed. If the aircraft is allowed to accelerate above 135...and, again, assuming you're accelerate/stop limited...you won't be able to stop the aircraft on the remaining runway. It's physically impossible.

Now, I know the FAA says you have two seconds reaction time...and all that $#%^...but, according to the engineers at Boeing...and they spoke to us directly at this seminar...above V1, (even only one knot above V1) the aircraft has too much energy to get stopped on the remaining runway.

This is why they (Boeing) recommend and profess that the V1 call be made before V1...so that the pilots have sufficient time to react...to begin the RTO (and deceleration) process BEFORE the aircraft is allowed to accelerate above V1. Once the aircraft is allowed to attain a speed above V1 (maybe even only one knot above V1), the braking capability will be insufficient to stop the aircraft in the remaining distance of the runway. (Assuming, again, you're accelerate/stop limited)

Thank you, again, for your input. Again, I know little about the engineering/certification aspect of all of this. But, I do remember my old airline having several accidents related to this. And, this was why Boeing sent a team to 'educate' us. And, what Boeing had to say was (to me) startling. I guess it was an eye-opener to the airline management as well, because our SOPs changed to match Boeing's recommendations within months after this seminar.

Thanks again...


Tom

[rhovsquared]

http://www.faa.gov/regulations_policies/rulemaking/committees/arac/media/aco/ACO_AP_T1.pdf please enjoy all 78 pages:} now y'all will understand what I mean by US gov't speak:{

just want to add very interesting discussion... if this keeps up i'll be in PPRune rehab!!!

[mutt]

Tom,
Just to focus on contaminated runways for a while. This is one of my little points of contention where I feel that the FAA should provide certification and operational regulations for operations from contaminated runways.
You won’t find an AFM page with contaminated runway definitions nor performance data, it just doesn’t exist. In the same way the wonderful electronic Flight Manual for the B777 won’t produce contaminated runway data as it just isn’t required under FAR25.
JAA regulations require operators to account for runway contaminants, JAR operators are therefore provided with contaminated runway data in the Flight Manuals. The best that the FAA has come up with is a 20 year old Advisory Circular based on a NASA test program using a Convair 880. AC91-6A is used as the basis for the data that Boeing provides in the Operations Manual and their non-certified computer programs.
So you are left in the quandary,

There are NO Federal Aviation Regulations pertaining to contaminated runway operations.
The FAA provides definitions and performance data in the form of Advisory Circular 91-6B.
The manufacturer hasn’t flight tested the aircraft on contaminated runways
The manufacturer offers “advisory” data.
Your airline accepts it as SOP.


So what’s your defense in an accident investigation?
Mutt

[TomConard]

Mutt,

Yes, you're right about contaminated runways and performance specs.

In the case of my old airline, we used V1min for not only contaminated runways, but wet and damp runways as well.

As far as my defense is concerned...I follow my company's SOP...which is approved by the local Air Carrier District Office. If any heads are to roll, it'll be above my pay scale. As part of the requirements to qualify for the AOC, my airline must publish SOPs. It is required that these be approved (and enforced) by the
FAA of our jurisdiction. (In this case, the PIT ACDO) And, I am legally bound to follow these SOPs, regardless of FARs, Boeing/Airbus certification criteria, etc.

As an example, I was flying a four-day trip. On 'day three', we were passing through Philly (our base) coming out of San Juan on our way to DCA. We had maybe an hour on the ground in Philly, so we hit the crew room and emptied our mailboxes (to clean out the stuff that had accumulated over the past three days). In our mailboxes was a Jepp revision (which wasn't there when we left Philly three days before). So, we grabbed that, headed back to the aircraft to saddle up for the short leg to Washington.

When we got back to the aircraft, there was an FAA inspector who was catching a ride back to DCA. He checked our licenses, medicals...the whole enchalada...including our Jepp manuals. When he found we were one revision behind...and had the revision envelope in our hot little hands, he went ballistic.

I explained to him the situation. Nevertheless, he insisted he was going to violate us. I told him that the system of Jepp revision distribution was devised by people way above the food chain from me...and if he had any problem with that, he should feel free to contact our Air Carrier District Office in Pittsburgh. I gave him the name of our POI (whom I knew well), and told him to contact her.

I further explained to him that the way we do things is approved/sanctioned by the FAA office assigned to our airline...and, if he had any problems with this, he should contact the FAA administrator and our POI. "Good luck with your career advancement! I hear Anchorage is really not as bad as people say!"

He dropped the issue immediately!!! No kidding!!! (He elected to ride in First Class :> :> :> :>)

As the saying goes, "I'm just following orders, Sir!"

Ain't bureaucracy great!!!! :> :> :>


Tom

[rhovsquared]

mutt: I find that to be a terrible oversight by the FAA, don't you think that they should schedule this data? I mean even in GA contaminated runways are common, then they go on to try to blame pilots for overruns but without the appropriate tests it seems very unfair. did you ever write to ALPA or other groups concerning this issue and if so what about inciting you're colleagues to do the same. the data exists so why not give it to US pilots?

As an aside I have found this data in one of my books " Cold weather flying" By, Jeff R Griffen 6/10" slush
Type TOW (lbs) Rwy length increase
DC-8 251000 10%
B 707-100 247000 15%
DC-8 296000 14%
B707-300 296000 15%
Convair 880/22M 150000 15%

And: weight reduction:

B 707 140000 -17500
B 727 152000 -19800
B720 180000 -10000
B720 190000 -11000
Caravelle 110000 -11000

I know this is of little help nowadays other than a history lesson:)

[rhovsquared]

http://www.pprune.org/forums/showthread.php?t=9287

[mutt]

Yikes that forum thread was 5 years old.......................

J_T..... would you be so kind as to halt any discussions on contaminated runways here............ Post them in another topic so that we can focus on reducued V1's on dry runways. Thanks...


Mutt....

.. no idea how to do that in a tidy fashion, mate, but I guess a bit of cut and paste should achieve the end you seek ..

if we can use this thread for the dry case discussions please ....

[mutt]

Jambo Buana

does any EU airline drop V1 to its minimum value, ie VMCG plus 1kt when possible?

Little bit outside the EU, but the answer is NO. For dry runways, we stick to balanced field V-speeds.

Whilst the possibility of utilizing V1MIN exists using VMCG as the lower limit. I have never heard of anyone “arbitrarily” reducing V1=VMCG+1kts.

For example, using the B777 at MTOW

Min V1 = 157.4 KIAS
Max V1 = 163.0 KIAS
Bal V1 = 160.2 KIAS
V1MCG = 121.6 KIAS at 35.0 DEG C


Minimum V1 is 36kts higher than V1MCG, as this is the minimum speed where the takeoff can be continued, an arbitrary reduction of V1 to V1MCG+1kt will result in that aircraft failing to achieve 35feet at the end of the runway, I would even hazard a guess that it wont be flying at all!

I think that you need to chat with the AA DEC and request further clarification.


Mutt

[Jambo Buana]

Tom,

I flew with a Boeing test pilot of 30 odd years on a recent C1 flight. I asked him a few questions and then whinged about pilots having so many theories on things. This is his qwote back to me, "son, theories are like xyzholes, everyone has one." Pretty nice I thought.

But what I am getting at is, that even in Boeing they have different theories on what we are talking about. I specifically asked a test pilot who was head of training standards 737 about calling V1 early. She said not to, that there was a 2 second reaction time for Mr Average etc.. So as time goes by the Boeing symposium you were at becomes history (which will repeat itself of course) and as new people take up their posts they forward their own theories.

This is a great game isnt it?

[Jambo Buana]

Hi Mutt,

I was just taking it to the theoretical limit of Vmcg+1kt. There must be occasions where Vmcg would be a lot closer than 36kts to a min V1. A very light BBJ for example.

If you compare my question to, reducing weight to achieve a contaminated RWY takeoff and thereby reducing V1 by 15 to 20 kts, you could reasonably expect, on long runways, that there is bags of extra performance available that would allow operators to reduce V1 by 10 to 20 kts lets say. Now this would provide a real safety benefit as you wouldnt get a really high energy RTO and crews are exposed to less time during which an RTO can be initiated.

2/3 of overruns are rejected unnecessarily in the first place! ref Boeing takeoff safety training guide.

[Mad (Flt) Scientist]

If you compare my question to, reducing weight to achieve a contaminated RWY takeoff and thereby reducing V1 by 15 to 20 kts, you could reasonably expect, on long runways, that there is bags of extra performance available that would allow operators to reduce V1 by 10 to 20 kts lets say. Now this would provide a real safety benefit as you wouldnt get a really high energy RTO and crews are exposed to less time during which an RTO can be initiated.
2/3 of overruns are rejected unnecessarily in the first place! ref Boeing takeoff safety training guide.

Remember, though, that Vmcg, and the minimum V1 derived from it, are both pretty arbitrary numbers. There's no black/white divide that says that at V1min+1kt you are 'safe' - the wrong combination of circumstances could easily see you in the grass. For example, I just checked one of our test reports for Vmcg testing on a single type. For a speed spread of 1.5 kts the lateral deviation varies between 5ft and 40ft - and pretty randomly at that, the highest deviation is NOT at the lowest speed. If test pilots, briefed as to the test and expecting the failure, have such a wide variation in results, how large would it be applied to service pilots caught unprepared.

So if one were to adopt a policy of routinely lowering V1 to (near) the minimum value, one would be increasing the risk of runway excursions to side, perhaps as fast as the risk of overruns was r\educed. (It's analagous to the practice of widespread reduced thrust takeoffs, reducing the real margin of takeoff performance)