So Wonwee

This is a question that I found on aviationinterviews.net. What is balanced field length? I don't recall ever hearing this term. Is there another term used for this?

HSLD

The balance is basically that you can accelerate to V1 lose an engine and reject the takeoff and stop on the runway AT MAX GROSS WEIGHT.

At weights less than MAX you have excess runway available for stopping. The excess runway provides various options such as:

Optional V1
Cluttered V1
Reduced thrust takeoffs

A full discussion could easily fill a chapter of a book, but hopefully you get the concept.

dutch747

I would add one thing by saying just what the co-founder said but balanced means that your gross weight is such that your stopping distance equals the runway available hence the word "balanced".

Cubdriver

To expand the discussion, how long would it take to realize the actual loss of an engine. Balanced field probably assumes there is a specified amount of time needed to catch some gross anomaly, but how about the grayer kinds of areas. If you are watching TIT, torque and other meters and it vacillates rather than tanks how hard is it to decide?

There is a segment on youtube showing a goverment airliner somewhere in europe overrunning due to a sudden bird ingestion in one engine. It is clear in the video they were unsure what to do.

fly-efi

Balanced Field Length simply means that your accelerated stop distance is equal to your accelerated go distance. Most manufactures depict their tabulated takeoff data with the Balanced Field Length as this allows for the most takeoff weight with the least amount of runway.

There are two requirements for takeoff. (That is for a Jet)

Accelerated Stop Distance: The distance required to accelerate to V1, lose and engine, and abort.

Accelerated Go Distance: The distance required to accelerate to V1, loose an engine, accelerate to Vr, and climb at V2. The aircraft must cross the end of the runway at 35 feet.

rickair7777

Balanced field assumes a total failure (not feathered, for a prop).

It also provides a few seconds to recognize symptoms, make the decision, and execute the abort. It's really pretty easy to recognize cuz a total failure will produce big yaw...I don't look for ITT abnormalities, if the thing heads for the grass prior to V1, I abort.

A partial failure would still provide thrust, so even if you didn't abort you could still probably go flying. Personally I would abort for any sort of drama involving controllability, vibration, or multiple engine indications, without a lot of analysis.

APM145

The FAR takeoff field length, often called the FAR balanced field length, contains certain inherent safety features to account for engine failure situations. This takeoff field length is defined in several slightly different ways. Briefly, if an engine should fail during the takeoff roll at a critical speed, called the decision speed V1, the pilot is offered the option of two safe courses of action. He may elect to continue the takeoff on the remaining engines, in which case, the takeoff distance is defined as the distance from the point at which the takeoff run is initiated to the point where the aircraft has reached an altitude of 35 feet. In the second alternative, the pilot may elect to shut down all engines and apply full braking. The decision speed V1 is chosen in such a way that the sum of the distance required to accelerate to V1 and then decelerate to a stop is the same as the total distance for the case in which the takeoff is continued following engine failure. If an engine should fail before Vi is reached, the aircraft is usually brought to a stop on the runway; whereas, if an engine fails at a speed greater than V1 the takeoff is continued. The distances are based on smooth, hard, dry runway surfaces.


Good Luck

For more
http://www.hq.nasa.gov/office/pao/Hi...-468/app-h.htm

alvrb211

The 35ft screen height applies to dry runways only !
For wet conditions, the screen height may be reduced to 15ft.
All that happens here is the 48ft obstacle clearance is reduced.

AL

Borat Sagdiyev

Actually, if the airplane is equipped with an autofeather system, the applicant (usually meaning the aircraft manufacturer) can take a performance credit for a feathered prop as opposed to a windmilling one. I have flown a couple of turboprops that would probably not make their second stage climb gradients unless the propeller was feathered shortly after an engine failure.

Happy time!!

ryguy

I'm quite certain if I am watching TIT, then I could care less about airplanes at that moment!