V2 & V2+15

[Manicured garden]

Hey guys, just a simple question.
I know there is a lot to talk about V2 and V2+15 speeds but I'd like to get the idea with least words. As a B737 pilot, at take-off, V2 and V2+15 speed bugs appear on PFD.

Could any of you please explain me why are they on there and what is the idea of these speeds?

Thanks in advance.

[ajd1]

You are a 737 pilot? Really? ..... If you Google V2+15 it will take you to a Pprune thread from Sept 2005 where it's all explained.

[JeroenC]

He didnt say he is. He asked it to us, 737 pilots.
(I cant check profiles here on the iPhone app). If you áre a pilot, hmmmmmmm.


Now, the answer: V2 is the speed your performance calculations are based on, and is the minimum speed at screen height after an engine failure. In our company it is also the speed to fly an ETP (emergency turn procedure).
V2+15 is the MAX speed you can fly engine out until acceleration height. Mr Boeing was nice enough to give us a bug for that.

Edit: V2+15 is the max speed

[RAT 5]

B737: V2 = Limited manoeuvrability = 15 degrees of bank + 15 degrees turbulence upset.
V2+15 = Full manoeuvrability = 25 degrees of bank + 15 degrees turbulence upset.

Therefore <V2+15 you can use HDG SEL at 15BA and at >V2+15 you can use LNAV and >15BA.

In the old days before speed tapes & FMC bugs you used to bug V2 & some companies V2+15 as well. It saved o the mathematics under stress. Now you have a 'picture'. Below the white bug 15BA, at or above white bug >15BA. Simple and very useful under stress.
ET is flown at V2 to maximise climb performance. It is the speed the obstacle clearance & turn radius is based upon. Therefore it is flown at 15BA. It's not quite true to say it is the maximum speed you can fly an ET at. Boeing did not invent ET's. It's all to do with manoeuvre margin and bank angle.

[Gysbreght]

I would have thought that V2 + 15 is the speed V2 + xx referred to in FAR 25.143(g), i.e. the airspeed approved for all-engines-operating initial climb.

V2 is strictly for one-engine-inoperative initial climb.

[JammedStab]

B737: V2 = Limited manoeuvrability = 15 degrees of bank + 15 degrees turbulence upset.
V2+15 = Full manoeuvrability = 25 degrees of bank + 15 degrees turbulence upset.



A lot of larger aircraft have this 15 degree bank limit below V+15 or V2+10 etc. Some aircraft have bugs to display this and some don't. Others have 15 degree bank angle limits when over a certain weight for a certain amount of speed above min flaps up speed.

[RAT 5]

Maybe so, and no doubt, Jammed Stab. I was being specific to the question about a particular a/c. I'm sure, due to aerodynamics, that all Perf A type a/c have such relationships.

What I am amazed about is how many long term B737 pilots (B757/767 in earlier days too) have no idea about this relationship. The same is true of why F15 & F1 is used for a G/A and what effect it has on bank angle etc. A serious gap in knowledge of the beast your riding.

[Alex Whittingham]

V2 is the minimum speed at which you can climb up to acceleration height, having lost an engine. It represents neither best angle nor best rate of climb but is a compromise 'minimum stagger away from the ground' speed that acknowledges that selecting a low pitch attitude to accelerate to best angle of climb speed after an engine failure would leave you with less vertical clearance from short range obstacles in the early climb.

Not knowing the B737, in general the all engines climb speed is V2+10, it may be V2+15 for the B737. This represents a speed that is easier to hold on all engines without extreme pitch angles and is closer to best angle of climb. In general the advice is that, although if you have an engine failure below V2 you should accelerate to and climb at V2, if you have an engine failure between V2 and the all engines climb speed you should hold the speed at engine failure, and this includes any emergency turn below acceleration height. In this scenario reducing to V2 would do nothing for you, it would reduce your climb angle and bring you closer to the stall. Is the 737 operated differently to this?

[RAT 5]

Guys: the questioner asked the meaning of, or why the bugs are there. I think we are getting too technical and can't see the wood for the trees. Most of the answer have concentrated on only V2. What about the significance of +15?

if you have an engine failure between V2 and the all engines climb speed you should hold the speed at engine failure, and this includes any emergency turn below acceleration height. In this scenario reducing to V2 would do nothing for you, it would reduce your climb angle and bring you closer to the stall. Is the 737 operated differently to this?

This now widens the discussion. There was a DC-10 out of Chicago who had a catastrophic engine failure after V2, lost some LED's, reduced to V2 as per SOP's, stalled & died. They had a flying aeroplane!
I flew for an outfit that taught ET's were flown at V2. If you have an engine failure after V2 the FD holds that speed in pitch. If there was an ET the company expected you to ignore the FD, reduce to V2 and fly the the ET. IMHO, daft. Fly the ET but keep what speed you have. It will be between V2 & V2+15. The climb performance and turn radius will be a gnat's cock the same. KISS!

[JeroenC]

Well, our books say ETP=V2, so yes, I would pitch ip to V2 if above.
Its not up to me to decide if its a gnats cock or not.
Was it concluded they would have survived if they maintained speed?

[RAT 5]

Well, our books say ETP=V2, so yes, I would pitch ip to V2 if above.

The problem with simple rules is they often only satisfy one condition, one scenario. This one is with an engine failure about V2. The geographical point can be assessed and the climb performance also. The turn radius can also be calculated, and the calculations are done (if memory serves me correctly) at max RTOW.
The FD will command V2. If you are V2 -V2+15 the FD will command that speed.
An ETP is written for the failure about V2. Does it advise what you do if the failure (bird strike) is at e.g. 500'? I doubt it. Do you need to perform an ETP? That is your decision at the time. Above what height does the ETP no longer apply? RTOW finishes at 1500' above aerodrome. The ETP is written for failure before V2 & 35' over the end of the runway (I think). So between 35' & 1500' with an engine failure you are on your own to decide what to do. If the ETP requires an immediate 180 turn, or short distance after rotate, to avoid obstacles/terrain straight ahead, but now the failure is well after rotate. You are closer to the obstacle than calculated. Do you follow the ETP 180 turn? It's not always so simple as you think.

The chance of being at Max TOW is small, so your performance should always be better than the assessment. Boeing state that the performance at V2 - V2+15 is the same: not my opinion. If you increase attitude to slow down you will not be following the FD pitch bar. You are already under stress with the engine failure. You might need all the help you can get; why ignore the FD? It will make your job harder. For the DC-10 they did not know about the missing LED's; i.e. they had a severe reduction in aerodynamic performance. What they did know is they had a flying a/c, and then they didn't.

[john_tullamarine]

Was it concluded they would have survived if they maintained speed?

P47 of the NTSB Report (http://www.airdisaster.com/reports/ntsb/AAR79-17.pdf) is relevant.

I flew for an outfit that taught ET's were flown at V2.

While that can be the case it is more general to predicate turns on a speed range. All depends on what the ops engineers do .. the procedure should specify the story for the line troops.

Boeing state that the performance at V2 - V2+15 is the same

Can't say that I've seen that .. do you have a reference ?

[Chu Chu]

Page 54 is relevant as well.

[RAT 5]

Hi John. Give me a few days when back at home and I'll dig it out. I have seen it in print---somewhere.

[Ivan aromer]

Seem to recall a DC10 that (literally) lost an engine. The crew reacted (as they had been taught) by pitching up to reduce to V2. Enfortunately they had also lost some slats and were unable to maintain control. It is suggested that had they maintained the speed at separation they would have maintained control. So I taught maintain the current speed UNLESS there is a chance of ground contact. It's all to do with energy conservation.

[Gysbreght]

More recent designs will comply with FAA Advisory Circular No. AC 25.1329-1C Approval of Flight Guidance Systems:

http://i.imgur.com/lVLoGV1.jpg?1

[sjm]

B737/300

Initial Climb - One Engine Inoperative The initial climb attitude should be adjusted to maintain a minimum of V2 and a positive climb. After liftoff the flight director provides proper pitch guidance. Crosscheck indicated airspeed, vertical speed and other flight instruments. The flight director commands a minimum of V2, or the existing speed up to a maximum of V2 + 20 knots. If the flight director is not used, attitude and indicated airspeed become the primary pitch references. Retract the landing gear after a positive rate of climb is indicated on the altimeter. The initial climb attitude should be adjusted to maintain a minimum of V2. If an engine fails at an airspeed between V2 and V2 + 20 knots, climb at the airspeed at which the failure occurred. If engine failure occurs above V2 + 20 knots, increase pitch to reduce airspeed to V2 + 20 knots and maintain V2 + 20 knots.


ETP Finishes once above MSA & calculated at V2+15kts

[RAT 5]

The discussion is becoming a little clouded reference the original question. That was why are there bugs for V2 & V2+15. That is to do with allowed manoeuvrability i.e. bank angle. Climb performance on 1 or 2 engines is another issue. The FD pitch bar will give guidance on that. If the FD is off and you have an engine failure then, yes, the bugs will be of significance. However, under normal departure ops the FD will be in view. You now have a choice of using LNAV or HDG SEL for routing, be it normal SID or ETP. If you are <V2+15 you need to use HDG SEL with 15BA max. That is the manoeuvrability issue. Climbing at V2-V2+15 is the obstacle and climb %gradient issue, which could be straight ahead or not. The speed has 2 effects, one lateral one vertical and they need to be understood individually.

[Gysbreght]

"... why are there bugs for V2 & V2+15"? The reason is simple:

V2 = initial climb speed with one engine inoperative, failure occurring before reaching V2

V2 + 15 = initial climb speed with all engines operating

The airplane must not be flown deliberately above or below those speeds in each condition.

Yes, the approved initial climb speed with all engines operating must provide manoeuvring capapability for up to 40 degrees of bank without encountering stall warning or other characteristics that might interfere with normal manoeuvring (ref. FAR 25.143(g)).

[eppy]

From FAA "lessons learned" report on AA 191 Accident:



The NTSB concluded that the airplane was being flown in accordance with American Airline's engine failure procedures. Immediately after liftoff, a pitch attitude of 14 degrees was attained and maintained, indicating use of the flight director for pitch guidance. It was also subsequently determined that the captain's flight director was inoperative, implying that the first officer was flying the takeoff. American Airlines procedures required that, following an engine failure, the airplane should be accelerated to V2, and climbed to 800 feet at that speed. No differences in the procedure were specified if an engine failure occurred after reaching V2, and in fact, the specific scenario was not addressed by the airline's procedures. Following the accident, American Airlines modified this procedure to either maintain the speed at the time of engine failure, if between V2 and V2 + 10, and to maintain not less than V2 + 10 if the failure occurred after reaching V2 + 10. The revised procedure also instructed crews to disregard the flight director pitch command (which provided guidance to achieve V2) and to maintain at least V2+10.
It was clear to the NTSB that the airplane was being decelerated from 172 knots toward V2 in an attempt to follow the engine-out climb procedure (and reacquire V2) when the left wing stalled at 159 knots. The stall resulted in the left roll and ensuing loss of control.

[winterOPS]

Pretty sure RAT5 is on the spot, regarding the original question. These limitations become very apparent when one is flying TP´s for instance the ATR has a very outspoken speed philosophy regarding the limitations on bank angle in respect of airspeed.

Found this in the FCOM for 73 classics as well....

Cheers W

https://www.imageupload.co.uk/images/2015/07/05/v2plus15_b737.jpg

[Derfred]

Hmmm... it seems V2+15 represents 2 things:

1. Minimum speed for full manoeuvrability; and
2. Minimum speed for all-engine takeoff (V2+15 to V2+25).

I wonder which one it is?

[Gysbreght]

I wonder which one it is?A bit of both, actually, although I wouldn't choose your exact wording.

There is also a third criterion. It is a speed that incorporates the speed increment that inevitably occurs, before the speed and flight path angle can be stabilized, when the airplane is rotated at VR at a normal rate with all engines operating, just as V2 incorporates the inevitable speed increment when rotated at VR with one engine inoperative.

P.S.

An additional consideration may result from FAR Part 36: Noise Standards, Appendix B:

(4) The takeoff reference speed is the all-engine operating takeoff climb speed selected by the applicant for use in normal operation; this speed must be at least V2+10kt (V2+19km/h) but may not be greater than V2+20kt (V2+37km/h). This speed must be attained as soon as practicable after lift-off and be maintained throughout the takeoff noise certification test.

[RAT 5]

I'd always thought V2 is a performance issue with all Perf A a/c. It is 'never below speed'; takeoff safety speed in old speak. Is it not related by various % to Vr & VMCA and perhaps many other speeds? It is a certification & performance speed for many types, as it is a concept.

Now for B737, and perhaps others, >V2+15 = full manoeuvrability.

One is vertical for all aeroplanes, the other is lateral for B737.

[winterOPS]

Yeah, bit of both....

Assuring margin for lift capacity enough during turn at a relatively low airspeed. Applies to different aircraft types t (wing planforms etc.) and different additives in airspeed, seems the norm is 10-20kt in this eg. B737 =+15 (less than +15 then a lower bank angle has to be used to not induce to much drag)


As for the increment just for climb (obstacle avoidance etc.) The all engine should give a better climb gradient compared to v2 only... as per briefing notes below...

https://www.imageupload.co.uk/images/2015/07/06/bus_v2_plus15_all_eng.jpg

[Gysbreght]

RAT 5:

This may refresh your memory:

Part 25 AIRWORTHINESS STANDARDS: TRANSPORT CATEGORY AIRPLANES
Subpart B--Flight
Performance

Sec. 25.107

Takeoff speeds.

(a) (...)

(b) (...)

(c) V2, in terms of calibrated airspeed, must be selected by the applicant to provide at least the gradient of climb required by Sec. 25.121(b) but may not be less than--

(1) V2 MIN;

(2) VR plus the speed increment attained (in accordance with Sec. 25.111(c)(2)) before reaching a height of 35 feet above the takeoff surface; and

(3) A speed that provides the maneuvering capability specified in Sec. 25.143(h).

[Gysbreght]

winterOPS:

Your figure 5 does not show an 'improved climb' V2 situation (refer to my reply to RAT 5 above).

[RAT 5]

Guys: This is a copy from B737 FCTM; as the original question was about this a/c. Note the comment that would suggest an ETP can be flown at the speed attained when the engine fails if >V2 & <V2+20.
See also the notes about bank angles v V2 (+15)

2 Engine normal takeoff.
V2 + 20 knots is the optimum climb speed with takeoff flaps. It results in the maximum altitude gain in the shortest distance from takeoff. Any speed between V2 + 15 and V2 + 25 knots results in approximately the same takeoff profile.
Note: A maximum bank angle of 30° is permitted at V2+15knots with takeoff flaps.

Engine failure during takeoff.
Adjust pitch attitude, as needed, to maintain desired airspeed of V2 to V2 + 20 knots.
The initial climb attitude should be adjusted to maintain a minimum of V2 and a positive climb. The flight director commands a minimum of V2, or the existing speed up to a maximum of V2 + 20 knots.
The initial climb attitude should be adjusted to maintain a minimum of V2. If an engine fails at an airspeed between V2 and V2 + 20 knots, climb at the airspeed at which the failure occurred. If engine failure occurs above V2 + 20 knots, increase pitch to reduce airspeed to V2 + 20 knots and maintain V2 + 20 knots until reaching acceleration height.
If an immediate turn is required, maintain V2 to V2 + 20 knots with takeoff flaps while maneuvering.
Note: Limit bank angle to 15° until V2 + 15 knots. Bank angles up to 30° are permitted at V2 + 15 knots with takeoff flaps. With LNAV engaged, the AFDS may command bank angles greater than 15°.

Thus: for B737 you will see that V2 - V2+20 (+25) is a general climb thing, while V2+15 bank angle limit is very specific. They are 2 different items. No doubt the manoeuvrability criteria was designed so that it combined well with the climb performance envelope. Sensible engineering.