What is one of the most important questions to be asking yourself before you takeoff? Do you have enough runway available to lift off safely? You don't want to be making planning decisions as they are happening. You want to have all your planning decisions made before your takeoff roll and focus on executing your plan to leave the ground safely. However, things don't always go as planned and you must be prepared to abort your takeoff, if necessary. How do you know when to abort your takeoff so that you have enough runway left to safely bring your aircraft to a full stop? The 50/70 Rule is a rule-of-thumb that many pilots use to mark a point to abort the takeoff without worry.
NOTE: The following does not apply for a takeoff with obstacles
The 50/70 Rule
Simply, the 50/70 Rule states:
If you have not reached 70% of your takeoff speed by the time you reach 50% of the length of the runway, abort your takeoff.
Let's work through an example of this assuming your aircraft is a Cessna 150 Commuter (Model 150M and maximum weight of 1600 lbs) and you're departing from Toronto City Centre Airport (CYTZ) Runway 08/26.
- Calculate 70% of your takeoff speed
- Maximum weight takeoff speed = 60 knots
- 70% of 60 knots = 42 knots
- Pick a halfway point on the runway
- Runway 08/26 = 3988 feet
- 50% of 3988 feet = 1994 feet
- Based on the Canada Flight Supplement (CFS), the approximate halfway point on Runway 08/26 is taxiway F (Foxtrot)
Therefore, if you don't reach 42 knots by Foxtrot, abort your takeoff. Since stopping your aircraft is much faster than accelerating, you will have plenty of runway to stop safely using the Engine Failure During Takeoff Run procedure, as outlined in your Pilot's Operating Handbook (POH). The diagram below shows the spot that you would abort your takeoff if you have not reached 70% of your takeoff speed.
To safely stop your aircraft, following the procedure below:
- Engine Failure During Takeoff Run
- Throttle - IDLE
- Brakes - APPLY
- Wing Flaps - RETRACT
- Mixture - IDLE CUT-OFF
- Ignition Switch - OFF
Have you used the 50/70 Rule personally? Share your experiences in the comments below.
