The rule is dangerous. Very dangerous. There is no bounding of the 50/70 ROT for runway length (extreme long or short), density altitude, or obstacles. Also, the 50/70 rule tells me nothing about stopping distance for abort considerations. Check out the Idaho Stinson crash from a few years ago. 5000' runway. I bet he had 70% of his takeoff speed at 2500' down the runway. It didn't work out. Into the trees. They lived but were extremely lucky.
I agree it's very dangerous, and I have actually contacted the FAA to have them review their reference to the "70/50" rule in the AIM. The 70/50 rule assumes constant acceleration, in which case distance travelled is proportional to the square of groundspeed achieved. So you would reach rotation speed at the very end of the runway if you had 70.7% of rotation speed at the halfway point of the runway. But acceleration is actually decreasing, because propeller thrust decreases with airspeed and aerodynamic drag is increasing. This means you won't even be at rotation speed at the end of the runway. This rule as stated is incredibly dangerous. Maybe it would be acceptable to say you should be at 75% of Vr by half of your calculated ground roll, but even then I would be cautious.
I noticed mixture was full rich. Some may say mixture should be at best power, which high density altitude may dictate leaning a little. But yes, every takeoff should have an abort point. Longer runways I use “if not rotating by calculated distance” even if I have plenty of runway left. Otherwise the 50/70 rules is great as long as ASDA allows.
I have a question. The 50/70 Rule, "establish a landmark at 50% of your calculated take off distance". For example, if calculated take off distance is 1000ft, shouldn't you stop by 500 ft if you cannot reach 40 knots at that point? Regardless of avail rwy distance. I tried to find some sources, like boldmethod or FAA. And found out that some are saying "50% of avail rwy" or "50% of calculated take off distance(FAA)" Which feels later option is more reasonable for me. So which one is the correct procedure?
So there two things here, that are similar but different. I will use terms from my Ops manuals, 1. Accelleration Check Point and 2. Safe Abort Point. This video is primarily referencing the acceleration check point, which is checking the aircrafts performance (power being produced, weight of the plane, density altitude etc). If the airplane is producing sufficent performance, you will accellerate to to 70% of TAKE OFF ROLL REQD, as demonstrated in this video. This is a performance based determination. I think, what you are reffering to, is what about if you are using a very long runway, seems silly to abort so soon. Well, in my organization, we also brief our Safe Abort Point. This is a point that, even if the airplane is performing well, we can abort the take off, and stop on the runway remaining. We brief it as "No further than 50% of RUNWAY AVAILABLE, adjust closer to the departing threshold as necessary" So, we could set out Safe Abort Point anywhere from Power Set/Brakes Release all the way to the 50% point, depending on any risks identified mitigated. One interesting point, the Safe Abort Point can be airborne. If you are using a 10,000' runway, in a GA airplane, you should be able to execute an abort from anywhere infront of the SAP, even if well airborne. We practice the maneouver, all the way up to the nominated point, its challenging but quite fun.
I think that the correct answer is probably the calculated takeoff distance, but as a practical rule of thumb, it is easier to use the available runway distance in scenarios where you will actually want to rely on the rule. For GA airplanes, the 50/70 rule should come into play when your available runway is close to your plane's takeoff performance, so those numbers should be close enough that it won't make much of a difference which one you use. If you have a general idea of how much runway you need for your plane at the elevations you typically fly during a particular season, then once you are near that number, give or take a thousand feet or so, you can do your calculations and apply the 50/70 rule to ensure you keep an eye out on when to abort. Conversely, if you are in a 172 on a 12,000-foot runway, whether you are or aren't thinking about the 50/70 rule, you will definitely notice if you aren't up by 6,000 feet even though 50% of your (un)calculated takeoff distance is behind you an entire county away.
@@JB_HobbiesBut you just know some pilot is going to be rolling down a 12,000 foot runway and hits 70% of Vr at 6,000 feet and thinks all is well but can't climb out of ground effect when he gets to the end of the runway.
So how we exactly know that we have used 50% of the runway because alot runways do not show that but can we really use Google earth to pick up landmark would it be helpful?
I had a rejected take off for real once. The throttle got stuck about half way so I wasn’t getting the full power I needed and I aborted take off. My instructor was so confused but I didn’t explain until I got off the runway
No. It’s not an incident in a GA airplane. At a towered airport, just tell the tower what you’d like to do next. If the controller is curious, he may ask what happened and if you need assistance. In most cases, it’s a non event. For heavy airliners it’s a little different, they may need to wait for their brakes to cool down and in some cases require an inspection before taking off again. The airline may require the captain to write a report but ATC doesn’t care unless there’s something that could impact other aircrafts. There should be no legal consequences in rejecting a takeoff and no pressure on the pilot to continue a dangerous takeoff.
@@jordanmccarthy1117 Sure. I'm not sure why someone would want the flaps up and elevator up. I am a new (currently ground-only) student but don't remember being taught that anywhere. In terms of aerodynamic braking aka drag, I'd assume you want the flaps down, but I understand why you would want more weight on the wheels and have them up instead. In terms of aerodynamic braking, I can understand why you would want the elevator up, but then there would be less weight on the wheels, which then is opposite of the advice for the flaps.
@@timothy-2614 As a student myself, I can say that we typically braked with fully extended flaps and elevator, but this may be model specific. Additionally, that was for a full stop landing when the speeds are much higher than in the middle of the takeoff roll. Additionally, at lower speeds, aerodynamic braking was negligible. Again, it may be model dependent, but I would guess that the lift from the flaps is working against the need for weight on the wheels. Additionally, in my trainer, the use of the elevator lifted the weight off the nose wheel, which made better use of the main gear. I would guess that drag is too negligible at those takeoff roll speeds, or at least the tradeoff of increased drag may not be worth risk having the brakes lock up from the lift of the flaps. I hope this helps! Again, I too am a student, so please take my opinion with a grain of salt. If an instructor wants to weigh in on this, would love to hear some thoughts!
@@jordanmccarthy1117 Thanks for your input. I pulled the "aerodynamic braking" reasoning straight from the video, so I can't comment on the validity of that.
@@timothy-2614 Jordan's right - flaps should be up to reduce lift so that more weight is on the wheels, as that's how you'll be stopping (braking effectiveness increases when there's more weight on the wheels). For take-off, at least in a 172, we'd have flaps up or, at most, 10 degrees (for a short-field t.o.). You see this same technique in short field landings - get flaps up, dynamic braking (elevator up), full brakes as needed.
This is NOT a good rule to use. It can put you at the VERY END of the runway for lift off. What about obstructions or contaminated runway or little less than optimal engine power? A better method is calculate take off distance using the POH and all pertinent information, add a safety factor and be able to abort with runway left over. (Landing distance also from the POH.) What about a 10,000 ft runway? Do you wait until the 5,000 ft mark to figure out something is wrong and you need to abort? Obviously not! So what length runway IS this rule good for? 4,000? 3,000?
Great points, and I would add that as acceleration is actually decreasing during the takeoff roll (propeller thrust decreases and aerodynamic drag increases with airspeed), you may not even be at liftoff speed by the end of the runway! The rule assumes constant acceleration, which isn't the case. I would say a better rule is that you should be at 75% of rotation speed by half of your calculated ground roll.
Excellent. Great balance of explaining what is critical while still being concise and clear!
The rule is dangerous. Very dangerous. There is no bounding of the 50/70 ROT for runway length (extreme long or short), density altitude, or obstacles. Also,
the 50/70 rule tells me nothing about stopping distance for abort considerations. Check out the Idaho Stinson crash from a few years ago. 5000' runway. I bet he had 70% of his takeoff speed at 2500' down the runway. It didn't work out. Into the trees. They lived but were extremely lucky.
I agree it's very dangerous, and I have actually contacted the FAA to have them review their reference to the "70/50" rule in the AIM. The 70/50 rule assumes constant acceleration, in which case distance travelled is proportional to the square of groundspeed achieved. So you would reach rotation speed at the very end of the runway if you had 70.7% of rotation speed at the halfway point of the runway. But acceleration is actually decreasing, because propeller thrust decreases with airspeed and aerodynamic drag is increasing. This means you won't even be at rotation speed at the end of the runway. This rule as stated is incredibly dangerous. Maybe it would be acceptable to say you should be at 75% of Vr by half of your calculated ground roll, but even then I would be cautious.
I noticed mixture was full rich. Some may say mixture should be at best power, which high density altitude may dictate leaning a little. But yes, every takeoff should have an abort point. Longer runways I use “if not rotating by calculated distance” even if I have plenty of runway left. Otherwise the 50/70 rules is great as long as ASDA allows.
Perfect as always ❤
Even the simulated video stressed my sphincter.
Thanks in advance, can you tell me the call sign or the ICAO designer for that airfield?
It's 2NC0. Added to the description
@@flightinsight9111 thanks for your reply
Could you add a link to this faa article?
I have a question. The 50/70 Rule, "establish a landmark at 50% of your calculated take off distance".
For example, if calculated take off distance is 1000ft, shouldn't you stop by 500 ft if you cannot reach 40 knots at that point? Regardless of avail rwy distance.
I tried to find some sources, like boldmethod or FAA. And found out that some are saying "50% of avail rwy" or "50% of calculated take off distance(FAA)"
Which feels later option is more reasonable for me.
So which one is the correct procedure?
So there two things here, that are similar but different. I will use terms from my Ops manuals, 1. Accelleration Check Point and 2. Safe Abort Point. This video is primarily referencing the acceleration check point, which is checking the aircrafts performance (power being produced, weight of the plane, density altitude etc). If the airplane is producing sufficent performance, you will accellerate to to 70% of TAKE OFF ROLL REQD, as demonstrated in this video. This is a performance based determination. I think, what you are reffering to, is what about if you are using a very long runway, seems silly to abort so soon. Well, in my organization, we also brief our Safe Abort Point. This is a point that, even if the airplane is performing well, we can abort the take off, and stop on the runway remaining. We brief it as "No further than 50% of RUNWAY AVAILABLE, adjust closer to the departing threshold as necessary" So, we could set out Safe Abort Point anywhere from Power Set/Brakes Release all the way to the 50% point, depending on any risks identified mitigated. One interesting point, the Safe Abort Point can be airborne. If you are using a 10,000' runway, in a GA airplane, you should be able to execute an abort from anywhere infront of the SAP, even if well airborne. We practice the maneouver, all the way up to the nominated point, its challenging but quite fun.
1:12 There’s 2 rules in the FAA document, the 50/70 and the 30/70 rule. Both are different. (Great question btw}
I think that the correct answer is probably the calculated takeoff distance, but as a practical rule of thumb, it is easier to use the available runway distance in scenarios where you will actually want to rely on the rule. For GA airplanes, the 50/70 rule should come into play when your available runway is close to your plane's takeoff performance, so those numbers should be close enough that it won't make much of a difference which one you use. If you have a general idea of how much runway you need for your plane at the elevations you typically fly during a particular season, then once you are near that number, give or take a thousand feet or so, you can do your calculations and apply the 50/70 rule to ensure you keep an eye out on when to abort. Conversely, if you are in a 172 on a 12,000-foot runway, whether you are or aren't thinking about the 50/70 rule, you will definitely notice if you aren't up by 6,000 feet even though 50% of your (un)calculated takeoff distance is behind you an entire county away.
@@JB_HobbiesBut you just know some pilot is going to be rolling down a 12,000 foot runway and hits 70% of Vr at 6,000 feet and thinks all is well but can't climb out of ground effect when he gets to the end of the runway.
@@igclapp That would be a very bad day
Great job!
So how we exactly know that we have used 50% of the runway because alot runways do not show that but can we really use Google earth to pick up landmark would it be helpful?
I had a rejected take off for real once. The throttle got stuck about half way so I wasn’t getting the full power I needed and I aborted take off. My instructor was so confused but I didn’t explain until I got off the runway
Does a rejected takeoff count as incident or something that needs be reported by ATC?
No. It’s not an incident in a GA airplane. At a towered airport, just tell the tower what you’d like to do next. If the controller is curious, he may ask what happened and if you need assistance. In most cases, it’s a non event.
For heavy airliners it’s a little different, they may need to wait for their brakes to cool down and in some cases require an inspection before taking off again. The airline may require the captain to write a report but ATC doesn’t care unless there’s something that could impact other aircrafts.
There should be no legal consequences in rejecting a takeoff and no pressure on the pilot to continue a dangerous takeoff.
@@Virtualmix Thanks!!
The whole flaps up and elevator up aerodynamic braking thing upon rejection wasn't clear.
Hello! Would you be willing to expound on what you wish were more clear?
@@jordanmccarthy1117 Sure. I'm not sure why someone would want the flaps up and elevator up. I am a new (currently ground-only) student but don't remember being taught that anywhere.
In terms of aerodynamic braking aka drag, I'd assume you want the flaps down, but I understand why you would want more weight on the wheels and have them up instead.
In terms of aerodynamic braking, I can understand why you would want the elevator up, but then there would be less weight on the wheels, which then is opposite of the advice for the flaps.
@@timothy-2614 As a student myself, I can say that we typically braked with fully extended flaps and elevator, but this may be model specific. Additionally, that was for a full stop landing when the speeds are much higher than in the middle of the takeoff roll. Additionally, at lower speeds, aerodynamic braking was negligible.
Again, it may be model dependent, but I would guess that the lift from the flaps is working against the need for weight on the wheels. Additionally, in my trainer, the use of the elevator lifted the weight off the nose wheel, which made better use of the main gear. I would guess that drag is too negligible at those takeoff roll speeds, or at least the tradeoff of increased drag may not be worth risk having the brakes lock up from the lift of the flaps.
I hope this helps! Again, I too am a student, so please take my opinion with a grain of salt. If an instructor wants to weigh in on this, would love to hear some thoughts!
@@jordanmccarthy1117 Thanks for your input.
I pulled the "aerodynamic braking" reasoning straight from the video, so I can't comment on the validity of that.
@@timothy-2614 Jordan's right - flaps should be up to reduce lift so that more weight is on the wheels, as that's how you'll be stopping (braking effectiveness increases when there's more weight on the wheels). For take-off, at least in a 172, we'd have flaps up or, at most, 10 degrees (for a short-field t.o.). You see this same technique in short field landings - get flaps up, dynamic braking (elevator up), full brakes as needed.
This is NOT a good rule to use. It can put you at the VERY END of the runway for lift off. What about obstructions or contaminated runway or little less than optimal engine power? A better method is calculate take off distance using the POH and all pertinent information, add a safety factor and be able to abort with runway left over. (Landing distance also from the POH.) What about a 10,000 ft runway? Do you wait until the 5,000 ft mark to figure out something is wrong and you need to abort? Obviously not! So what length runway IS this rule good for? 4,000? 3,000?
Great points, and I would add that as acceleration is actually decreasing during the takeoff roll (propeller thrust decreases and aerodynamic drag increases with airspeed), you may not even be at liftoff speed by the end of the runway! The rule assumes constant acceleration, which isn't the case. I would say a better rule is that you should be at 75% of rotation speed by half of your calculated ground roll.
You did not mention leaning for that altitude which most likely would have helped greatly.
It was noted and demonstrated in the conclusion