15' Screen Height

[extreme P]

I believe it is predicated on a two engine aircraft being given credit for single engine reverse when it comes to stopping on a contaminated runway. How does this apply to a three or four engine airplane? Same screen height and how many reversers are credited?

[rhovsquared]

It seems to me that your confusing a few issues let me see if i can clarify this a bit.
1. as far as the 15' screen height: during a performance limited DRY RWY TO if an engine fails after V1 (takeoff decision speed) the minimum height that that a jet is "allowed by law" to cross the screen is 35' by that height and (by law) the speed of the aircraft must be V2 (TO safety speed), by THAT height 35'. during operations on WETor contaminated rwy's attempting to stop at the actual V1 will probably cause you to overun the rwy, so a reduction from the DRY V1 becomes necessary. so a few knots is knocked off the dry V1 i.e. V1- 10 Kts. This decision results in a performance penalty whereby, you end up over the screen (in the worst case scenario) crossing the screen as low but NOT LOWER THAN 15' agl. However you still must reach the safety speed V2 by 35'(by law).
2. The concept you seem to be confusing is the accelerate stop with the take off distance available (ASDA vs TODA) when determining the former in dry conditions reverse thrust is not factored in on dry RWY's but RT is allowed in determining the WET distance.
3. With all that said I've probably mixed up something and there are many here who are MUCH more qualified to respond to your query than me as I don't yet fly jets, but I'm nevertheless in love with them and don't care to much for high performance/complex or multiengined piston aircraft but those are expensive and jet training costs even more not, so easy to follow that passion. gotta stick with biochemistry and molecular bio and Piper Warriors for now.
4. Almost all questions about jets are answered by the book by David P. Davies, Handling the Big Jets Third edition (70-150$). Got mine from Australia long ago; if you're not hooked after he does 'Stalling' you need your head examined

Hope some of this helped Rhov:)

[extreme P]

The question is: how much reverse is a three or four engine aircraft given credit for and what is the screen height? Nothing more, nothing less.

[FlapsOne]

15' agl..............................surely not!

[rhovsquared]

Same as a twin..........surely yes, that's the wet V1 penalty

[mutt]

This decision results in a performance penalty whereby, you end up over the screen (in the worst case scenario) crossing the as low but NOT LOWER THAN 15' agl. However you still must reach the safety speed V2 by 35'(by law). Interesting, but could you please supply the appropriate FAR to back this up!
My understanding is that you reach V2 at 15 feet and thereby your Net Obstacle Clearance is 15 feet, at no time do you revert back to 35 feet clearance!
extremeP, Credit for 3 engine aircraft = 2 engines, 4 engine aircraft = 2 engines on opposite sides.
Its worth noting that some manufacturers produce their data based upon ZERO thrust reverse for twin engine aircraft. Boeing provides both 1 engine reverse and Zero engine reverse for the 777.
Mutt

[rhovsquared]

"The FAA proposed to revise Sec. 25.113 to allow the distance required for a continued takeoff from a wet runway to include taking off and climbing to a height of 15 feet, rather than the height of 35 feet required on a dry runway. This lower screen height (which is the height of an imaginary screen that the airplane would just clear with the wings in a level attitude when taking off or landing) would reduce the balanced field length V1 speed, thereby reducing the number of high-speed rejected takeoffs on wet runways. The FAA considers lowering the screen height to 15 feet to be an acceptable method of reducing the risk of overruns on wet runways because of the similarity to current rules when operating from dry runways that have a clearway. The minimum height permitted over the end of the runway for current dry runway takeoffs may be 13 to 17 feet, depending on the airplane, when a clearway is present. In addition, a 15-foot minimum screen height and vertical obstacle clearance distance has been allowed for many years by the United Kingdom Civil Aviation Authority for wet runway operations without any problems being reported". perhaps not here yet Davies is British, but it makes sense.........I said (basically) the SPEED V2 MUST BE ACHIEVED BY 35' REGARDLESS OF THE LOWERED SCREEN HEIGHT!!!

[mutt]

So you are basing your information on the book Handling the Big Jets Third edition (70-150$)?

Mutt.

[rhovsquared]

no that vide supra is the proposed reg. FAR that is and ...... yes that book is a true masterpiece and timeless but i've read many many many many other book AIM/FAR the FAA AFM and the IFM ,Aerodynamics for Naval Aviators, Weather flying and Instrument Flying and the PTS's Boeing 727/757-200/747-200 AFM's, Janes All The World's Aircraft,...Cold weather flying Multiengined Flying, Flying Glass the Turbine pilot's Handbook and many many more and I started this path around since about 10 years old...I truly love aviation:ok:

[Old Smokey]

To view the topic from a horizontal rather than a vertical perspective, V2 must be reached by the end of the Takeoff Distance. The legislation (FAR 25 and all of it's equivalents) requires that.

The same legislation also requires that, at the end of the Takeoff Distance, a screen height of 15 ft (Wet Runway), 35 ft (Dry Runway), or 50 ft (turning manoeuvre) be achieved.

Putting those two statements together, V2 must have been achieved at or by the time that the applicable screen height has been reached.

The reason that I included the "or by the time" phrase into the last sentence is that for turning procedures where 50 ft screen height is required, the manufacturers don't provide separate data for the 50 ft case, and some of the 1st Segment must be considered for the 35 ft to 50 ft climb whilst still within the TODA, and the 1st Segment is conducted at V2, in short, it's already been achieved (in this case).

Regards,

Old Smokey

[john_tullamarine]

yet Davies is British

.. not sure whether Davies was British but, if I recall reading this along the way a long time ago somewhere, did he not live in Neath (NSW, lower Hunter Valley just out of Newcastle) as a youngster ?

[OverRun]

DP Davies: I think there is both a Neath in South Wales aka UK, as well as a Neath in NSW aka Dunnunda & Godzone. I suspect the UK one. Not wishing to hijack the topic, so v. briefly: David Davies was born in 1920 at Neath in South Wales. Joined the Royal Navy in 1940, later commissioned in the Fleet Air Arm. Joined the Air Registration Board in August, 1949, as Chief Test Pilot and carried out the certification testing of the world's first jet transport aircraft in 1950. He has since been responsible for the certification flight trials of most British civil prototypes and a number of the larger validated aeroplanes (incl Concorde).

[john_tullamarine]

... another fondly held belief shot down in flames ....

[Woomera]

And IMHO his outstanding work "Handling the Big Jets" should be a primer for the CPL and part of ATPL syllabus.

It contains the most succint descriptions and explanations of basic and high speed flight and the evolution of transport category certification philosophy as you will find in one book.

It was written, as those who have read it will know, for pilots transitioning from old technology piston and turboprop to the new fangled turbine thingummies.

It is as fresh and valid today as it was then.

[MrBernoulli]

From the 2004 reprint of Handling the Big Jets:

"David Davies was born in 1920 at Neath in South Wales ..... now lives at Wickwar in South Gloucestershire."

[Luke SkyToddler]

There was a thread here on PPRuNe at the time, the great man sadly passed away in Nov 2003. I'm sure his work will be required reading for new jet pilots for many many years to come yet.

... from Air Safety Week, Jan 12 2004

David Davies, famed chief test pilot of the UK's Civil Aviation Authority (CAA), died Nov. 30 at age 83. His obituary appeared in the Jan. 1 edition of the London Times. Over his 33-year career with the CAA, Davies flight-tested airliners ranging from the turboprop Viscount to the supersonic Concorde. Of his experience qualifying Concorde, Davies said, "Our job was to ensure that Concorde could be flown home from Mach 2 at 60,000 ft. after a range of double failures such as engines, computers and hydraulics, and landed with no undue skill or strength."

In addition to his achievements as a test pilot, Davies authored one of the seminal books about flight safety, "Handling the Big Jets." A copy of the 1990 third edition is "Reference A" in the small but selective library of this publication. Perhaps no other book has had such an impact on educating pilots on the why's and wherefore's of flying jet-powered airliners. It is a timeless masterpiece of engineering discourse and flying advice made plain.

[oldebloke]

Here we go again:Handling the big jets covers the BCAR (the original WET 15'screen height proponent)..'Aircraft performance Theory for pilots'pj swatton. covers todays EASa rules(exam questions)
As stipulated The US.FAR's now refer to the Wet 15'screen-But only the B777 conforms to the new standard, as no one ,ATA/FAA/Builders would supply the AFM data(Boeing has it at a cost for the offshore operators(non FAA)'B' package)..Under EASA rules one gets 'reverser' credit in the Wet acc/stop operation(Airbus FCOM)..If reversers are inoperative one gets a payload penalty...
The B777 performed the 'actual'tests(flown)on WET runways,unlike 'analysis'
performance which had been added in the passed(SAS DC 9 etc)
cheers.
:ok:

[rhovsquared]

It seems as if the FAA is behind the power curve again with data on only one type, what is the point of proposing that anyway? I'll definitly check out that performance book that Oldbloke has mentioned soon. Does the US now have "two out" acountability (ferry V2's etc.) data for quads during three engined ferries or is a second failure still suicide under FAR's? for little planes FAA's not too shabby get lots of relative freedom. Finally, I retract that "V2 must be reached by 35' " statement altogether...I've been schooled
Davies did write that, obviously things have changed; I thank Old Smokey for clearing up that misconception for me. I read lot of posts from the two performance experts here, John_Tullamarine and Old smokey, and feel truly enlightened each time:)

[rhovsquared]

I mean I retract the statement "V2 must be reached by 35', regardless of the lowered screen height-statement"....I hate typing.

I didn't realize Davies passed away...very saddened....always wanted to meet him... guess in another lifetime...yes the book will remain a masterpiece until we are beamed over the ocean or we all have "pilotless-nuclear-powered-travel-pods"
the key word being "pilotless"