Hello. Is there a good publication explaining not only what are those four segments of take off, but also why they have their criteria. Specifically, V2 during second segment. E.g. what happens if V2 is significantly exceeded during the second segment? Any mathematical models or real flight tests used to prove it?
Thanks.

 

Did you try Google?

https://aviatorsguide.wordpress.com/...limb-segments/

https://skybrary.aero/articles/engin...y-jet-aircraft

https://www.youtube.com/watch?v=I4HyKKvptAo

 

Of course, I did. And didn't find the answer to my question (including in the links you provided). This is why I asked it here.

 

Not sure if this answers your question at all or maybe I’m not understanding what you are asking. V2 is not the normal climb speed if that is what you are thinking when you are reading about these segments. We regularly climb just after takeoff at a speed that is at least 20kts above V2 until flap retraction. The airplane still flies and climbs well and you can really get as fast as the maximum flap speed which is very far above V2. The only time we would climb at V2 on a takeoff is if an engine is lost after V1.

 

I fly an airplane which by SOP requires ~ V2 + 10...15 kts in the second segment. This is normally still well below flap retraction speed, so flap speed is not a factor. I've flown with a couple of pilots who intentionally fly at V2 + 40..50 and it's also is not a factor for flaps speed. They do reach flap retraction speed by doing so but they don't exceed it. However I think that's not an optimal climb (much more drag (power of two of speed)). I wonder if there are some publications that explain it in details, not just as a general idea.

 

Start with this, for a primer: https://www.faa.gov/documentLibrary/...r/AC120-91.pdf

First segment is screen height (35') until gear retraction, at which time second segment begins. Understand that the purpose of climb segments is terrain and obstacle clearance following an engine failure after takeoff. At that point, all other factors are largely irrelevant (nose abatement, etc). Procedures for climb after takeoff, and the certification and performance criteria that drive them, all focus on obstacle clearance. If you step outside the design elements of each climb stage, then you invalidate the required performance around which the airplane and its planning charts, software, etc, are designed.

While V2 represents takeoff safety speed, an additional buffer is included for two primary reasons. One is that often one will be past V2 at the time of an engine failure, or during a normal takeoff. V2 + 10-15 is "close enough," and will still give that necessary climb performance through flap retraction (second segment until flap retraction, but at a minimum, through 400'). Maneuvering may or may not be required below 400'. Some aircraft have bank angle restrictions at V2, which are mitigated by a higher speed, up to 15 knots higher, allowing full maneuvering bank angle. This, in turn, allows reduced turn radius, to allow a turn for obstacle clearance while maintaining an adequate airspeed margin (otherwise provided by V2 in a wings-level climb).

Excess speed above this maneuvering margin (typically +10-15 knots) increases turn radius such that benefits from the increased bank angle are reduced or eliminated. Further, higher climb speeds reduce climb performance at a time when the primary mission is to maintain control while increasing terrain separation as efficiently as possible. Because one is departing the surface, where obstacles begin, getting away from the surface obstacles in the minimum distance (as opposed to minimum time) is the priority. This is a geometry exercise. Angle beats rate. We want a steep, but safe climb, and a fast climb defeats that effort. Accelerating to V2+50 does not provide the steepest climb away from obstacles, at a time when flap retraction is not the goal. Obstacle separation is. Travel faster forward, climb less steeply, and one covers more ground while climb less: this means a shallower climb angle, or a lesser climb gradient.

When considering takeoff weight, our weight isn't just limited by runway available, but by other factors, including climb performance after takeoff, and obstacles in the takeoff and and climb path. Hence, "runway analysis" which accounts for all of that (and for dispatching purposes, destination and enroute runways, environmental conditions, yada, yada). Alter your climb by adding fifty knots, and all that goes out the window. If you're departing over the water with no obstacles, perhaps not so critical, but second segment climb and obstacle clearance doesn't provide an unlimited value.

Where no obstacle departure is provided for a runway, the obstacle-free climb gradient must allow a minimum of 200'/nm climb away from that runway, in all directions. That's not a lot. It's notable, however, because obstacle paths and protection don't begin until something penetrates that obstacle clearance plane; it becomes more detailed with regard to second segment climb performance, certification, and allowable performance under Part 25 certification, but the point is that there isn't an inherently generous obstacle clearance margin to begin with. Compromise that by flying outside the parameters established for your aircraft and your operation, and you may find yourself too close to objects, too soon. At V2+15, for example, you may may have 25 degrees bank available for maneuvering, and still have adequate climb ahead with an engine out, based on the anticipated angle of climb. At a much higher speed (eg, V2+50, for example), one may leave that obstacle clearance plane, fly farther, flatter, and thus compromise the safety of the flight. Again: this is about geometry: angle of climb. You gain nothing by accelerating to V2+50, if the second segment climb is planned at V2 to V2+15, and you do sacrifice your obstacle clearance. the idea is to get up and away from obstacles, then accelerate and clean up. Accelerating to higher speeds, greater than what is required for safe bank angle maneuvering margin, hurts your climb, and doesn't provide anything of value.

Typical engine-out plans climb to 1000' or a pre-determined flap retraction altitude, using the second segment climb speed. Second segment begins with gear retracted and continues to a minimum of 400, from which point, for certification purposes, acceleration to flap retraction speed is presumed to begin. A runway analysis will determine at what altitude flap retraction is allowable (400' being minimum), with most procedures being typically 1,000 or higher. Many don't turn until 1,000, but that really depends on the runway and obstacles.

Typically V2 is the climb speed, plus whatever margin is cited (typically 10-15 knots). If the pilot has reached a higher speed, in some cases manufacturers dictate that up to that speed, maintain that speed, but no more . So, if the allowance is V2 to V2+15, but the manufacturer states up to V2+25, then one shouldn't be conducting that second segment, all the way up to whatever flap retraction altitude is to be used for that particular departure. If one winds up at V2+20, then keep it. If one winds up at V2+30, pitch slightly to reduce to V2+25...but don't exceed the speed prescribed for that segment, until flap retraction altitude. Remember, geometry. Angle. Faster climb, shallower angle. The maximum speed given (such as V2+25) is the fastest one should go for that segment, until flap retraction; faster only defeats that gradient.

This presumes the engine failure at the surface, with the first segment beginning there, until gear retraction. It presumes the climb is being conducted with an engine out, or reduced climb thrust from a failed engine. Obviously with that engine providing thrust, the values change, and one will be climb faster, with both a faster rate and angle. We plan our performance and our path, however, on a thrust loss, and the ability to make that departure safely with the thrust loss, in addition to the normal departure on which we plan. If everything is working, the issue of second segment becomes academic; the moment thrust is lost, however, it becomes crucial. It's well and good to compromise the numbers when all is operating...but we conduct the departure the same each time and respect those numbers because we have planned for them, and because we know they work, and because we do not know when they will be needed.

 

My SOP target (OEI) is V2+20. That provides a margin above flap maneuver speed (V2+15), to allow for any special procedure turns at normal turn rate.

As others have said, V2 is not the target speed, it's more of a safety floor.

 

Brain dead but wasn't Airbus' SOP V2+10 and Boeing allowed V2+15-25??? It's been decades but Boeing put something out that said "V2+ X (15? 25?) still gave adequate climb performance despite the excess speed. Now this is where the 'brain dead' really kicks in - was that Boeing saying "it's okay with BOTH engines operating" but with single engine V2+ 10 (15?) was the upper limit?

 

Depends which Boeing. Generally in Boeing the initial climb is V2 to V2+15; some require an additional bank margin, some don't, and that's true of certain variants or models of the same type. It's not a one-size-fits-all for Boeing.

 

That was a very useful summary for someone new to the concept of "climb segments" but I'd like to put a finer point on this one.

Before the crash of AA191 (May 1979), industry standard practices were to maintain V2 through second segment climb (even with engine failure).

But this video is an excellent description of how that past practice didn't account for any flap/slat malfunction.
https://youtu.be/e3lzgrFuM4s?si=B_ha2QpBEmVkGVSI

After this accident, industry practice changed to climbing at V2+10 (or +15) until acceleration height in order to provide additional margin above stall speed in case of flap/slat malfunction.