Take-Off Segments

A_Pilot · March 21, 2015

Hey, I recently saw a post on here where everyone was debating through their ears about what's what in a takeoff. Now granted that the various jurisdictions have varying rules and standards, take-offs are pretty darn similar from one country to another. Here's a quick guide to takeoffs, and what goes into getting the plane into the air from a performance standpoint (not hitting things):

All-Engines Operative Take-Off (stupid simple):

Cross the Threshold of the runway at at least 35 feet
Don't turn below 400ft AGL
Climb at 200ft/nm, (3.3% gradient), or at a gradient that's listed in the SID for obstacle clearance requirements.

One-Engine-Inoperative (OEI): (for an EOSID)

Basics:

V1: Takeoff decision speed: the speed higher than which you're taking your emergency in the air

V2: The speed you target when first in the air with that aforementionned emergency. Designed to get you above obstacles in a pinch.

Vlof: Speed your tires come off the ground.
TORA: The chunk of ground where your tires are allowed to be for take-off. Usually the length of the runway from where you enter it.
TODA: The point at which you need to be at least 35 feet in the air and at V2, assessed with gear down or transitioning upwards. This distance = TORA + Clearway

LEVEL OFF: The altitude at which it is safe to begin your acceleration and transition to the enroute phase of your climb. (Flaps up, Bleed air on, etc). At this altitude required to have cleared a close-by obstacle. Higher of 400' or obstacle clearance altitude.

Now, The five parts: GROUND ROLL, SEGMENT 1, SEGMENT 2, ACCELERATION, and SEGMENT 3.

GROUND ROLL begins with application of Take-Off power/thrust, and ends when your wheels come off the ground. Here you'll find V1, Vr, Vmu, Vle, Vlof, Vmcg, and an engine failure. Also hydroplaning speed.

SEGMENT ONE begins when your wheels come off the ground and ends when your gear is fully retracted. Somewhere in here you'll probably find the end of your TODA, and that 35' requirement mentioned above (in some countries this drops to 15' with wet runways). Applicable speeds from here on are V2, V3, Vxse, Vmca, Vle, Vlo. This segment exists because of the decreased climb performance when the landing gear extended. Not usually restrictive because it's so short time-wise.

SEGMENT TWO begins when your gear is fully retracted and ends when you reach your assessed Level Off altitude. Commonly the most restrictive segment in one-engine-inoperative climb calculations because of the reduced power/higher drag/low terrain&obstacle clearance. The goal of this segment is something like: "Let's not hit that close by tree/building/hill"

ACCELERATION begins at Level Off, and ends when you've reached the next applicable climb speed. It is a LEVEL segment (no climb). In this phase, you feather your engine (for you prop types), clean up your flaps, and get to a more appropriate speed (Climb speed, Best Rate One-Engine-Inop, etc - depends on the plane) Here you typically calculate the distance it will take to complete all of this from the end of the runway to the point where you start SEGMENT 3. in order to see if you clear the obstacles in SEGMENT 3

SEGMENT THREE begins when you reach the speed mentioned in ACCELERATION and ends when you reach the altitude where you're considered in the enroute portion of your climb. This means either 1500 above the ground, the Minimum Safe Altitude, Minimum Vectoring Altitude, far out Obstacle Clearance Altitude, etc.... After this point you're no longer considered taking off, but rather climbing enroute.

If you've been paying attention, you'll notice the 3 main segments all pertain to different configurations of aircraft:

Segment 1: Flaps T/O, Gear down, (+ prop unfeathered / auto-feathering)

Segment 2: Flaps T/O, Gear up, (+ prop unfeathered / auto-feathering)

Segment 3: Flaps up, Gear up. (+ prop feathered)

For performance calculations, airlines need to prove that they can clear the obstacles that fall within the lateral distance of all this with an engine out. In the absence of any obstacles, there are minimum climb gradients that must be achieved in each particular segment. These gradients vary if you have 2,3,or 4 engines on a normal day, and are subject to a variety of penalties.

For example: SEGMENT 2 usually has for required gradient 2.4%, 2.7%, and 3.0% GROSS for 2, 3, and 4 engines respectively. On top of that, a 0.8%,0.9%, and 1.0% buffer is required to allow for sucky flying. SEGMENT 3: 1.2%, 1.5%, and 1.7% GROSS. SEGMENT 1: "Positive climb" So like, 1 inch per million nautical miles or something.

GOOD NEWS: The charts take all this into account (for the most part). the programs all know these rules.

So: If your plane has "Certified Engine Out Performance" - the chart will show the 2.4/2.7/3.0% GROSS gradient (perfect flying). Take off the applicable buffer and you get a NET take-off path of 1.6,1.8, and 2.0% (crummy flying). This NET path must clear things by 35'.

Punch in your numbers, and come up with your figures, be it your derates, your TODR, your ASDR, or whether or not that runway works at all!

Hope this has instructed at least 3 of you, to have made it worth my time

A_Pilot · March 22, 2015

Hey, I recently saw a post on here where everyone was debating through their ears about what's what in a takeoff. Now granted that the various jurisdictions have varying rules and standards, take-offs are pretty darn similar from one country to another. Here's a quick guide to takeoffs, and what goes into getting the plane into the air from a performance standpoint (not hitting things):

All-Engines Operative Take-Off (stupid simple):

Cross the Threshold of the runway at at least 35 feet
Don't turn below 400ft AGL
Climb at 200ft/nm, (3.3% gradient), or at a gradient that's listed in the SID for obstacle clearance requirements.