NORMAL TAKE-OFF

LESSON OBJECTIVES

  1.  Before Departure Checks

  2. The T/O Briefing

  3. Learn Normal T/O and After T/O Procedures

  4. Factors that affect the T/O distance

Image by Ryan Johns

-Before Departure Checks-

Before departure, there are some procedures designed to check that all essential systems such as the engine, the instruments,..etc are working properly. These checks are specifically for each type of aircraft and the POH must be checked in each case for clarification.

For example, in the Cessna 172, the Before T/O checklist is:

1. Parking Brake -- SET 

2. Cabin Doors and Window(s) -- CLOSED and LOCKED

3. Flight Controls -- FREE and CORRECT

4. Flight Instruments -- SET

5. Fuel Selector Valve -- BOTH

6. Mixture -- RICH 

7. Elevator Trim -- TAKEOFF

8. Throttle -- 1700 RPM

9. Magnetos -- CHECK (RPM drop should not exceed 125 RPM on either magneto or 50 RPM differential between magnetos)

10. Carburetor Heat -- CHECK (for RPM drop)

11. Engine Instruments and Ammeter -- CHECK

12. Suction Gage -- CHECK

13. Avionics Power Switch -- ON

14. Radios -- SET

15. Flashing Beacon, Navigation Lights and or Strobe Lights -- ON as required

Now that we know how to perform the required checks and what must be revised, our next objective is to understand the reason for these checks:

- Parking Brake -> Ensure that the aircraft is completely stopped as our attention will be focused on doing the checks

- Cabin Doors and Windows -> Even if there is an airspeed below which it is possible to keep the windows open. It is not recommended to do so. In any case, if one of the doors is open during T/O. the best course of action is to continue the departure, land as soon as possible and close the door

- Flight Controls -> It is our last opportunity to check that the ailerons, elevator and rudder are working properly. Do not only move the control column but also check that the corresponding movement of the control surfaces is correct

- Flight Instruments -> Check that altimeter is calibrated properly, the attitude indicator is stable and the directional gyro is aligned with the compass reading

- Fuel Selector and Mixture -> With the fuel selector in both and the mixture in Full Rich position we reduce the possibility of engine failure on T/O due to fuel starvation

- Elevator Trim -> The trim has a predetermined position for T/O to prevent the aircraft to be trimmed excessively nose-down or nose-up, which could difficult the control of the aircraft

 

The steps defined from points 8 to 12 are the run-up procedure. A run-up is a series of checks performed by pilots to check the engine and other systems dependent on it like the alternator or the vacuum pump.

- Throttle -> The throttle is used to set a predetermined value of RPM to check the engine reaction at power settings higher than idle

- Magnetos -> The magnetos control the spark plugs of the cylinder. To check change the setting from BOTH to LEFT and observe if there is an RPM drop between the limits prescribed on the POH. Then, repeat the operation with the RIGHT setting and also compare the RPM difference between LEFT and RIGHT settings. Excessive or no RPM variation means that the left or right magneto is not working properly

- Carburettor Heat -> In icing conditions, there is the possibility that the carburettor system starts creating ice which could end in an engine failure. When the carburettor heat is activated, unfiltered air from the outside is heated by the exhaust gases and directed to the carburettor melting the ice. As the air is heated, its density reduces, making the engine produce less power. You should note an RPM drop when carb heat is on

- Engine Instruments and Ammeter -> Instruments are checked to confirm that the engine is operating under normal values. The ammeter is checked to assure that the generator is charging the battery at a normal rate

- Suction Gauge -> Some flight instruments like the attitude indicator use a gyroscope that turns at high speeds thanks to a vacuum pump attached to the engine. The suction gauge measures the vacuum produced by this pump, if it does not reach a minimum value, the flight instruments dependent on it will work abnormally

- Avionics Power Switch -> Avionics Power must be on to send electricity to the radios and transponder, which are essential for the ATC to safely control the traffic of the airspace

- Radios -> Correct frequencies must be set to allow the communication between the pilot and the ATC. But also in the case of using NAVAIDs to navigate

- Flashing Beacon, Navigation Lights and or Strobe Lights -> In the Departure Checks it is supposed that you are about to enter the runway in a short period. Turning the different lights on (depending on the situation), help the other traffics to see you and avoid a collision in time

-The Take-Off Briefing-

The take-off briefing is a small talk given to the other pilot in case of flying during instruction or to ourselves in case we are flying solo.​ In this briefing, we discuss the normal procedure applied on the T/O reviewing things like the flaps setting, the callouts, the airspeed used...etc.

After the normal procedure is discussed and adapted depending on the conditions (meteorology, traffic ..etc). The emergency procedures are mentioned. The reason is to have a fresh knowledge of the possible situations and in case one of them occurs, react rapidly and efficiently.

Normal Procedures Briefing:

Today, the active runway is 23, the wind is 230º/ 5 kts, the flaps setting that we will use is 10º

 

Once we are aligned with 23, we will set full power and call out "T/O Power Set"

As soon as the Airspeed Indicator gives an indication, we will call out "Airspeed Alive"

At 30 kts, we will check that engine parameter are normal and callout "Engine Parameters in Green"

At 50 kts is our rotation speed, after lift-off, we will continue the climb at Best Angle of Climb Speed (Vx) which is 65 kts until 400 ft AGL

After 400 ft AGL, we will accelerate to the Best Rate of Climb Speed (Vy) which is 70 kts and retract the flaps, perform the After T/O checklist. Then continue climbing to "............ ft" and proceed to "......" point

Emergency Procedures Briefing

In case of any abnormality before the rotation speed

- Reduce power to idle and maintain directional control with the rudder. Apply the brakes as required to stop the aircraft, secure the aircraft and communicate the situation to the ATC

In case of engine failure below 500 ft AGL and sufficient runway

- Reduce power to idle and lower the nose to maintain Best Glide Speed (Vglide) which is 60 kts, extend the flaps as required and land on the remaining runway and secure the aircraft

In case of engine failure below 500 ft AGL and insufficient runway

- Reduce power to idle and lower the nose to maintain Best Glide Speed (Vglide) which is 60 kts, find a place to land 30º left or right from your current flight path

In case of engine failure above 500 ft AGL

- Reduce power to idle and lower the nose to maintain Best Glide Speed (Vglide) and start a 180º turn in the direction of the wind to land on the opposite runway

-Normal Take-Off Procedure

We have performed the required checks and discussed the course of action in the T/O Briefing. We are aligned with the active runway and clear for takeoff. It is time to see in detail how we manipulate the controls to make the aircraft leave the ground:

As an aircraft is designed to fly, the takeoff is fairly simple, but some details must be discussed to do it properly

- Once we are aligned with the runway, we will increase the throttle to maximum power, the increase in power must be done smoothly to minimize engine stress, the common rule used is that taking the throttle from idle to full should take 3 seconds

- A situation with high power and low airspeed is the perfect scenery for two of the left-turning tendencies (Review Lesson Nº1 - Basic Aerodynamics) to appear (the torque and spiralling slipstream). These tendencies will produce a turning motion on the aircraft to the left during the T/O run, which must be corrected with the right rudder pedal to maintain the runway centerline. As the aircraft accelerates, the torque and spiralling slipstream effect reduce and the rudder pedal requires less pressure

- As the aircraft accelerates the airspeed indicator is checked along with the engine instruments. In case the airspeed indicator is inoperative or one of the engine parameters would be outside limits, the T/O should be aborted

- The aircraft reaches the rotation speed (VR), which is the speed at which we must start applying slight back-pressure on the control column to lift the front wheel of the aircraft. This movement increases the AoA of the aircraft which combined with the low airspeed increases the effect of another left-turning tendency, the P-Factor, as you increase back-pressure a simultaneous right rudder input may be necessary to maintain the aircraft perfectly coordinated.

-The lift-off speed (VLOF) is the speed at which all the aircraft leaves the ground completely and its weight is transferred from the main wheels to the wings.

Normal Take-Off Profile.png

- After lift-off, confirm that the aircraft is at a positive rate which means altimeter indication increasing and positive rate of climb indication. As the aircraft is near the ground, obstacles could be a consideration, so the Best Angle of Climb Speed (Vx) that gives us the most altitude gain using the less horizontal distance possible, must be maintained. Remember Lesson Nº 5 - Climbs and Descends,

- Once a safe altitude, like 400 ft (AGL), is obtained and the obstacles are cleared, lower the nose to increase the airspeed to the Best Rate of Climb Speed (Vy) that give us the most altitude gain per unit of time, retract the flaps and perform the corresponding After T/O Checklist of the aircraft. For example: 

- Flaps -> Up

- Landing Light -> Off

- Electric Fuel Pump -> Off

- Usually an altitude of 500 ft AGL is used to turn towards the crosswind part of the circuit. In this case, we will suppose a left-hand circuit. Take a reference 90º to your left and perform a left climbing turn with a maximum bank angle of 20º while maintaining Vy. Stop the turn when the reference is in front and separate a precautionary distance from the runway.

- Once there is enough distance between the aircraft and the turn, take another reference 90º to your left to proceed to downwind and perform:

- Left Climbing Turn -> Maintaining Vy and at a max. bank angle of 20º if you have not reached yet the circuit altitude (1000 Ft AGL)

- Left Level Turn -> Maintaining a moderate speed and at a max. bank angle of 30º if you have reached your circuit altitude (1000 ft AGL)

- To ensure that enough distance is maintained between the aircraft and the runway use visual clues:

- Low-wing Aircraft -> The wing-tip must appear touching the runway

- High-Wing Aircraft -> Divide the wing braces in 3, then 2/3 of the brace must appear touching the runway

Traffic Pattern.png

-After Take-Off Procedure

-Factors affecting T/O Distance-

Before starting the discussion about these factors. First, we must define some basic concepts:

- Take-Off Run -> The horizontal distance along the takeoff path from the start of the takeoff to the point at which VLOF is reached

- Take-Off Distance -> The horizontal distance along the takeoff path from the start of the takeoff until the aircraft reaches 50 ft (or 15 m). In some special cases, this altitude requirement can be lowered to 35 ft

- T/O Distance = T/O Run + Distance to reach 50ft

From these definitions, we can imply that all the factors that affect the climb performance as we saw in Lesson Nº5 - Climbs & Descents. All factors that affect lift, weight, thrust and drag affect the aircraft performance during take-off

- Altitude -> ↑ Altitude -> ↓ Air Density -> ↓ Thrust -> ↓ Excess Power -> ↓ Acceleration -> ↑ T/O Run and Distance

- Temperature -> ↑ Temperature -> ↓ Air Density -> ↓ Thrust -> ↓ Excess Power -> ↓ Acceleration ->  T/O Run and Distance

- Humidity -> ↑ Humidity -> ↓ Air Density -> ↓ Thrust -> ↓ Excess Power -> ↓ Acceleration ->  T/O Run and Distance

High, hot and humid is a good mnemotechnic to remember the factor that adversely affects our take-off and climb performance

- Weight -> ↑ Weight -> ↑ RCW-> ↓ Excess Power -> ↓ Acceleration ->  T/O Run and Distance

Flaps -> Low flaps setting give a high increase in lift per a small drag penalty. The extra lift reduces the airspeed required for lift-off but the drag penalty decreases the climb performance. Flaps would be very useful in a short runway with no obstacles ahead, for example

Flaps vs  No Flaps.png

Wind -> Aircraft generate lift with speed, but the speed required is not measured in reference to the ground (groundspeed) but reference to the speed of the air (airspeed) flowing over the wings. With a headwind, more air is flowing over the wing reducing the necessary speed over the ground to take-off. In tailwind conditions the opposite occurs, we need more ground speed to compensate for the higher speed of the air in the same direction

Headwind vs Tailwind.png

What differentiates the T/O and the climb? Exactly, for take-off, you need a runway and the conditions of this runway (terrain, slope ..etc) also affect the takeoff distance:

Slope -> This is very straightforward. A downslope runway reduces the take-off distance because part of the weight of the aircraft acts forward in the direction of thrust improving acceleration. An upslope runway creates the opposite effect

Terrain -> A concrete runway is the standard. But, if in any case, you have to take-off in an unpaved strip such as ground or grass, there is a detrimental effect on the take-off distance due to the greater resistance that this type of terrain has, which create a detrimental effect on aircraft acceleration