n-1 Missed Approach Climb Gradients - help

[bohpilot]

Hi,

I have to explain the following.

Why on a Two Engine jet is the single engine Missed Approach Climb Gradient 2.1%, when the certificated minimum is 2.5%. Why do we allow a lower climb gradient.

Is it just a fudge to get though certification.....

[pstaney]

In the US, the missed approach gradient is "terped" for 2.5%. This means all obstacles are below this 2.5% slope, which is a 1:40 slope. Exceptions are noted in missed approach climb gradient requirements on the jepp chart, the last time I looked Burbank California was one.

Terps doesn't consider engine failure, decreased performance due to ice build up, or any other aircraft problem. It just provides a gradient, or altitudes that are clear of obstacles. Among other things.

FAR 25 requires the manufacturer to demonstrate a minimum of 2.1% for 2 engine aircraft, in the approach configuration that the manufacturer wishes to use, with an engine out. Of course, if this is not best gradient, then if you are in the same configuration as a take off, flight at V2 assures you of 2.4%, as long as you read your weight/temperature/altitude chart correctly.

And as you've pointed out, there is a disconnect between the 2 parties. What's the use of ensuring 2.1% climb gradient, yet the missed approach instructions require 2.5% to be clear of obstacles? Left hand of the government not talking to the right hand. And these certification numbers are so old, they just don't make sense in today's environment.

Stan

[bohpilot]

Thanks for that, I presume that over here in Europe JAROPS applies the same standard.?

[FlightDetent]

The CAT II/III approach gradient is 2,5%.

Still do not understand the 2,1 vs 2,5 thing.

[pstaney]

Boh, I "think" it's the same in Europe. You'll notice that quite a few missed approach instructions in Europe give you a minimum climb gradient. What I don't know is whether this gradient (the few places in the US, and Europe) gives you a buffer over obstacles, for eg 48 feet per nm. SID's in the US do just that, provide this 48 feet per nm buffer.
The manufacturer's 2.1% certification for approach climb, and the 2.5% for V2 are the same I'm quite sure between JAA and FAR25. I guess I don't know whether a missed approach in Europe, without any climb gradient explicitly stated on the plate, would provide any safe margin over obstacles if one were to fly a 2.5% missed approach gradient.

[bohpilot]

I am sure they are the same, but I have heard that for my captains board exam this can come up as a question.

Now I think I have it straight in my mind, but how to explain it in one easy sentence is another matter.....Any thoughts

[wondering]

I reckon, regulatory requirements and the actual airport design requirements don´t always make a lot of sense.

On take-off, have you ever wondered why second segment climb on a twin is only 2.4% when the procedure design gradient is 3.3% (2,5%+0,8%)? On the other hand, as long as the aircraft clears all obstacles by 35' we are ok. So, 2.5% (still 0.1% more than second segment climb) should be alright as long as the aircraft is crossing screen height at 35'. Still, where does the procedure design gradient with its 0.8% margin figure in?

And to complicate things further, on a wet runway screen height is reduced to 15'. Meaning the aircraft won´t clear obstacles by 35' for a while. I wonder how long the aircraft is allowed to fly with less than 35' clearance.

Sorry if I hijacked your thread. Just wanted to point out other related 'irregularities'.

[locust]

ICAO has elected o present the climb requirement for a SID in a slightly different fashion.They specify in DOC 8168, PANS-OPS, Aircraft Operations, a minimum climb gradient of 3.3% for the same segment of the flight.

A quick calculation shows, that these two climb requirements (FAA AIM 200' and ICAO) actually are identical.
1 nautical mile=6.076 feet, so 3.3% equals 200 feet per nautical mile.
This 200 feet per NM way of expressing the minimum permissible climb perfomance for all SIDs where a crossing altitude or a higher gradient is not prescribed, is very convinient for use in the cockpit.

in other words, when flying a SID, you are only guaranteed not to hit anythingif you climb with at least 3.3% or 200 feet per nautical mile until reaching the MEA.:)

[pstaney]

in other words, when flying a SID, you are only guaranteed not to hit anythingif you climb with at least 3.3% or 200 feet per nautical mile until reaching the MEA.:)

I think you would be guaranteed 48 feet per nm clearance.

[oldebloke]

On a normal T/Off one is configured to the optimum flap, ergo the 2.4% climb gradient!(engine out).
On a normal go'around one is configured to the 'near' landing flap setting of DRAG(one setting less than full"go'around flaps")ergo one need only demonstrate a 2.1%gradient climb.
If one performs a CAT2 approach(at normal landing weights)one must demonstrate a 2.4% climb gradient.(aircraft lower to the runway???)
IF one is required to perform a 2.5% Gradient one must go into the Manual/FCOM and reduce to the weight to meet THAT gradient
FCOM 3.5.35 Airbus.
Cheers.:ok:

[john_tullamarine]

A case of apples and oranges and wishful thinking here ....

There are

(a) aircraft design standards (things required by FAR23, FAR25, etc),

(b) airports design standards,

(c) operational standards

and so forth ..

... and no basic reason why any should consider the others.

It is up to the pilot and/or operator to make sure that the aircraft's capabilities on the day (and as delivered by the aircraft design standards) are constrained (where necessary) to provide the (sometimes more critical) capability standards prescribed elsewhere.