MasterOfPuppets

I’m agreeing with you not calling you out

89Pistons

I could be mistaken but I believe autobrakes 1 through 4 give you a rate. RTO will give you maxium no matter what. RTO doesn't care about the rate.

82spukram

there is a rate associated it’s just not obtainable by the system so it maintains maximum brake pressure. (Airbus was 10 m/s squared, I don’t know if I have ever seen a 737 number for RTO setting). Weather you use reverse or not you will be able to achieve the rate associated with RTO (737) or max (320) if you reject and they activate so get the maximum pressure the brake system can apply.

Knotcher

yup

it never ceases to amaze my how many pilots have no idea how the brakes work.

Knotcher

Not really making sense. On the 737, RTO just applies max pressure to the brakes period. Any reverse added goes on top of the stopping power of the brakes.

82spukram

I was pointing out that all auto brake setting including RTO work the same. A rate is programmed for each setting (RTO, 1,2,3,Max). RTO value is not attainable by the aircraft braking and reverse thrust system so the only thing the system can do is apply maximum pressure. You are correct its max pressure I was just pointing out the system logic is attempting to achieve a rate that the engineers put outside the airplanes capability.


i just noticed in my previous post I left out the word not. As in you will not be able to achieve the rate. It changes the entire post. Sorry about that. I can no longer edit it.

Guppydriver95

This is in no way meant to be a smart a$$ response. But are you really surprised? Look at how both carriers(all carriers for that matter) train systems. Watch some CBT’s and pass a test for which most people have the gouge. The days of a Socratic style back and forth with a live instructor teaching systems are gone, driven by the bean counters. So no, I’m not surprised at all that things like this are not common knowledge.

cougar

To my knowledge, technical bulletins reside only on MyBoeingFleet under Flight Ops, Bulletins and Newsletters, and Flight Operations Technical Bulletins. MBF access is limited to individuals approved by their respective companies.

cougar

RTO is maximum braking, equivalent to pushing on the brakes with maximum force. It is not a deceleration rate. For example, 75/76/747 Autobrake deceleration rates are AB1 = 4 ft/s2, AB2 = 5 ft/s2, AB3 = 6 ft/s2, AB4 = 7.5 ft/s2, and MAX AB = 11 ft/s2 (I don't know the 737 numbers). RTO, however, is 3000 psi hydraulic system pressure applied to the brakes to achieve maximum braking. Reverse thrust typically will not decrease the stopping distance on a dry runway but only reduce the energy the brakes absorb.

Boeing airplanes are certified per FAR 25-7, which requires speedbrakes and maximum manual braking (after the brakes have been heated up). Reverse thrust is not used to determine acceleration-stop performance on a dry runway. As such, RTO must equal Maximum manual braking for certification performance.

Airplanes certified after amendment 92 can use wet data for acceleration-stop performance, in which reverse thrust credit can be used. On a wet runway (or contaminated), reverse thrust decreases the stopping distance proportional to the runway condition code (i.e., the lower the RwyCC, the more thrust reverse helps), as anti-skid systems would increasingly release brakes for a skid. Conversely, the brake torque limiter would release brakes at heavyweights and dry runways to prevent exceeding the maximum torque on the wheel axle.

Consider the FAR takeoff performance requirements. Calculating takeoff accel-stop performance would be nearly impossible if RTO functioned as a deceleration rate.

Sliceback

Boeing HUD's (737/787) display a de-acceleration rate. With spoilers deployed at max reverse 737's generate 2.75 de-acceleration rate. 787's achieve 3.5 (3.75??). It decreases as speed decreases. With full reverese thrust the 737 drops below 2 at approx 100 kts*. The 787 drops below 3 at approx. 130 kts and below 2 at apprrox. 90 kts*. It's easy enough to check as you can feel the autobrakes being applied if you're using autobrakes 2 (737/787) or autobrakes 3 (787@130 kts).

So selecting 2 on the autobrakes doesn't apply the brakes until roughly 90-100 kts if you're using full reverse thrust.

* - it might be 90 kts on the 737 and 80 kts on the 787.