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Performance’ certifications

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Performance’ certifications

Old 12th Dec 2020, 22:28
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Performance’ certifications

On B777 we used to say that if you have take off performances then you’ll be able to land whatever the overweight (landing distance)
A guy told me it’s the same thing on A320 due to certification duties
Is anybody able to confirm ?
Thanks
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Old 13th Dec 2020, 09:44
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Originally Posted by larigo View Post
On B777 we used to say that if you have take off performances then you’ll be able to land whatever the overweight (landing distance)
A guy told me it’s the same thing on A320 due to certification duties
Is anybody able to confirm ?
Thanks
What circumstances are you referring to? Standard all engines return to land? OEI? Hydraulic failure?
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Old 13th Dec 2020, 20:51
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Originally Posted by larigo View Post
On B777 we used to say that if you have take off performances then you’ll be able to land whatever the overweight (landing distance)
A guy told me it’s the same thing on A320 due to certification duties
There is nothing like this required for certification of aircraft, and I'm pretty sure this theory quickly loses solid ground when the runway is contaminated, a significant amount of stopway is available, runway has a displaced threshold, etc.
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Old 14th Dec 2020, 13:20
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There are certification rules which address elements of this - for example 25.735(f) discusses "return to land" failure scenarios in the context of brake KE:

(Guidance material)
The critical landing weight for this condition is the maximum take-off weight, less fuel burned and jettisoned during a return to the departure airfield. A 30-minute flight should be assumed, with 15 minutes of active fuel jettisoning if equipped with a fuel jettisoning system.
Since part 25 doesn't explicitly require consideration of contaminated runways during design, it would be surprised if the contaminated case were explicitly or consistently addressed for such a scenario, though.
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Old 14th Dec 2020, 18:46
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Discussed several times.

The stopping requirement for landing (LDR), with at least the same amount of flaps used for take-off, is always less than the ASDR requirement. For the latter the most critical case being V1-stop with all engines operating.

Distance is not an issue unless non-normals come to play or the pavement friction degrades significantly.
Structurally, the weight is never an issue.

The trouble lies with the approach climb gradient. The lowest certified landing flap may be more than the one used to depart and the 2.1 (certification) 2.5 (PANS OPS) might not be there. Hence the performance OEI for GA becoms an issue for the longhaul types with a large difference between MTOM and MLM. In other words, if the T7 can do it, the 320x certainly will too.





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Old 14th Dec 2020, 19:17
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As Mad Scientist notes - it's called "Return to Land" - and it is a cert requirement, although the specifics themselves are rather vague.
The scenario is that there is some undefined emergency right after a MTOW takeoff that means you need to return to land as soon as possible, well above the max landing weight - fire, major hydraulic failure, etc. However since the nature of the emergency is undefined, you don't need to account for the consequences of the emergency - e.g. longer stopping distances because a hydraulic failure took out some of the brakes (you do want the pilots to be on their 'A Game' though).
It's generally not a limiting case, but it is something that is taken into consideration during the certification process.
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Old 14th Dec 2020, 22:14
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Sounds like the "Return to Land" as described by M.(F).S. defines the need (or not) for a jettisoning system. Possibly as performance VS. the landing climb requirement?
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Old 15th Dec 2020, 03:15
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I wrote this the last time this subject came up. Some of it may be helpful here.


The regulation that determines whether a jettison system is required is 14 CFR 25.1001(a). It has nothing to do with the relationship between max takeoff weight and max landing weight. The requirement for a jettison system is instead based on climb capability at a weight equal to max takeoff weight minus the weight of fuel necessary for a 15 minute flight consisting of a takeoff and return to land. If the climb gradient requirements of sections 25.119 (all engine climb in the landing configuration flaps down gear down) and 25.121(d) (engine out climb in the approach configuration flaps down gear up) cannot be met at this weight, then a jettison system is required by 25.1001(a).

The flow performance of the jettison system, if required by 25.1001(a), is required by 25.1001(b) to be able to get the airplane within 15 additional minutes to a weight that allows the airplane to meet the climb gradient requirements of 25,119 and 25.121(d).

The braking system regulation, section 25.735, sets the energy absorption capability requirements for the brakes. Landing at max landing weight at anticipated speeds must be withstood repeatedly as normal operation with no damage other than normal wear. Landing at max takeoff weight must be withstood without hazard, but parts can be destroyed or require inspection/maintenance. The structural regulations (25.473) set the landing loads that must be met by setting descent rates that must be accommodated as limit loads at max takeoff weight (6 feet per second descent rate at touchdown) and at max landing weight (10 feet per second descent rate at touchdown). A design can be limited by the braking and structural regulations to a maximum landing weight that is significantly less than the maximum takeoff weight, and whether or not a jettison system is required would have nothing to do with this. It's all design choice - how strong do you want to build your gear and brakes, and what climb performance do you want to provide.

Of course, performance information (climb gradient and runway distance) for landings in excess of the maximum landing weight up to the max takeoff weight is required to be provided in the AFM by 25.1587(b)(3).
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