Gross ceiling Net ceiling?

[Flyman35]

what is gross ceiling and net ceiling?

[Old Smokey]

If you're referring to One Engine Inoperative (OEI) performance, and I assume that you are :-

Gross Ceiling is the maximum Altitude / Level that may be maintained OEI with the remaining engine/s at MCT, and the aircraft flown at recommended Drift-Down speed. The Climb Gradient is (obviously) 0%.

Net Ceiling is the maximum Altitude / Level that may be achieved OEI with the remaining engine/s at MCT, and the aircraft flown at scheduled Drift-Down speed where the Climb Gradient is 1.1% (2 engined aircraft). Similar rules apply for the OEI en-route Climb.

In short, the 1.1% Delta between Gross and Net is the performance degradation OEI that we are accustomed to in other areas such as 2nd Segment Climb (in this case 0.8% for a 2 engined aircraft), or the artificial lengthening of the 3rd Segment.

The practical application of the 2 ceilings are that Gross Ceiling may be used for Flight Planning purposes, TAS, Fuel Flow etc. Net Ceiling is used to ascertain en-route Terrain clearance for the OEI "escape routes" en-route, or, where the original route may be maintained, that Net Ceiling equals or exceeds MEA. In level flight at the Net Ceiling, the 'normal' 1000 ft terrain clearance applies, but this is increased to 2000 ft during Drift-Down.

[Flyman35]

thanks old smokey for the information.would you refer me to a book which has all mentioned information.

[Old Smokey]

Flyman35,

Required Reading : USA - FAR 25, Europe - JAR 25, Australia - CAO 20.7.1B:ok:

There are others:)

[FE Hoppy]

Europe is CS-25 these days. It's free online somewhere official.

[Old Smokey]

Thank you FE Hoppy, afraid all my work is FAR 25 and Australia. Do you or anyone out there have a link please?

[Flyman35]

Old Smokey thanks for your help.Thanks for all friends.

[javelin]

It's that strange area you climb into when Shanwick only offer you 340 or 380 and you are too heavy for 380 but give it your best shot anyway :ok:

Bless the 330, what a machine !

[FlightDetent]

EASA Certification Specifiaction, part 25:
Agency Measures | Certification specifications (http://www.easa.europa.eu/ws_prod/g/rg_certspecs.php#CS-25)

Due to legal status of EASA within EU, each and every document has a lot bureacratic ballast attached. Once you cut through, the document can be found, albeit not easily (I didn't find it on the site but needed to google it out):
http://www.easa.europa.eu/ws_prod/g/doc/Agency_Mesures/Certification_Spec/CS-25%20Amendment%206.pdf

[Miles Magister]

What a pleasure to see people being nice and helpful to each other on this site.

[john_tullamarine]

Required Reading : USA - FAR 25

.. et voilà .....

(a) FAR 25.123 (http://ecfr.gpoaccess.gov/cgi/t/text/text-idx?c=ecfr&sid=2aa59517cd2f58ed0341be0ec94e34b9&rgn=div8&view=text&node=14:1.0.1.3.11.2.155.19&idno=14)


(b) FAR 25.123 explanatory information from AC 25-7A (http://www.faa.gov/regulations_policies/advisory_circulars/index.cfm/go/document.information/documentID/74402)

18. EN ROUTE FLIGHT PATHS - § 25.123.


a. Explanation. This guidance is intended for showing compliance with the requirements of § 25.123 and application to the operating requirements of §§ 121.191 and 121.193, which specify the clearances over terrain and obstructions required of the net en route flight paths subsequent to the failure of one or two engines.

b. Procedures.

(1) Sufficient en route climb performance data should be presented in the AFM to permit the determination of the net climb gradient and the net flight path in accordance with §§ 25.123(b) and (c) for all gross weights, altitudes, and ambient temperatures within the operating limits of the airplane. This en route climb performance data should be presented for altitudes up to the all-engines-operating ceiling to permit the calculation of drift-down data in the event of an en route engine failure.

(2) Fuel Consumption Accountability. The effect of the variation of the airplane’s weight along the flight path due to the progressive consumption of fuel may be taken into account using fuel flow rates obtained from
airplane manufacturers’ test data. If measured fuel flow data is unavailable, a conservative fuel flow rate not greater than 80 percent of the engine specification flow rate at maximum continuous thrust (MCT) may be used.

(3) The procedures and flight conditions upon which the en route flight path data are based should be provided to the flightcrew. Credit for fuel dumping, if available and included in the flightcrew procedures, may be
used to achieve the performance capability presented in the AFM. A conservative analysis should be used in taking into account the ambient conditions of temperature and wind existing along the flight path. All performance should be based on the net flight path and with MCT on the operating engine(s).

(c) FAR 121.191 (http://ecfr.gpoaccess.gov/cgi/t/text/text-idx?c=ecfr&sid=1afede8905a697004feb54c290b817b2&rgn=div5&view=text&node=14:3.0.1.1.4&idno=14#14:3.0.1.1.4.9.2.11)

(d) FAR 121.193 (http://ecfr.gpoaccess.gov/cgi/t/text/text-idx?c=ecfr&sid=1afede8905a697004feb54c290b817b2&rgn=div5&view=text&node=14:3.0.1.1.4&idno=14#14:3.0.1.1.4.9.2.12)

.. with the presumption that you have far too much spare time on your hands and can wade through this stuff.

What a pleasure to see people being nice and helpful to each other on this site.

Perhaps not in every forum but we try to keep it nice in Tech Log and Safety CRM etc ..

[Old Smokey]

Just a small tip, stolen from Lufthansa's excellent Pilot Performance Training Manual. (One of the best for pilots in my opinion, QF is the better, but written more for aspiring Performance Engineers).

If you have to dump fuel to ensure OEI terrain clearance, begin dumping IMMEDIATELY upon commencing Drift-Down. That will ensure a much higher OEI ceiling. Leaving it until late in the Drift-Down, it may already be too late!!!!

[I-NNAV]

Hi everybody!
I decided to continue on this topic since few days ago I had a chat with a colleague about OEI ceiling requirements.
We where talking about in flight re routing or DCT to and he was sure that in flight we can accept these routings considering the obstacle separation based on gross ceiling, while I was pretty sure that even in flight we have to respect the net ceiling requirements: this on a low performance turboprop leads to really different capabilities.
I tried to check the easa and I didn't found where it states that we are allowed to use the gross ceiling and also getting grips with performances of Airbus doesn't state anything about.
Can someone tell me the exact CAP where finding this answer?
Thanks everybody!

[john_tullamarine]

Some comments -

(a) can't help with the reference unless I do the same research you can do .. when you find it, perhaps you can cite a link for the rest of us ?

(b) you will need to refer to the relevant State requirements for the specific rules

(b) normal requirement for multis (I presume you are talking heavy turboprop ?) is to cover the OEI case or else you will have route distance limitations

(c) for OEI planning, nett is whence the numbers need to come - otherwise we wouldn't worry about nett for takeoff and such.

[I-NNAV]

Hi John, thank you for your reply
A)I already check the above link (http://www.easa.europa.eu/ws_prod/g/doc/Agency_Mesures/Certification_Spec/CS-25%20Amendment%206.pdf) that is really complete but it's more related to the certification phase, my question is more operational related.
I also checked Airbus getting to grips with aircraft performance (http://www.skybrary.aero/bookshelf/books/2263.pdf) but it takes the info from the one above, so nothing new.
I google it but nothing emerged.

B)I'm interested in EASA requirements for CS25 twin turboprops

C) On the material I found is stated that in planning phase you have to use the net ceiling for en-route obstacle separation, we all agree, the doubt is about in flight replanning like a route change or a direct to.

[FE Hoppy]

You probably need to be looking in the AMC to Part CAT. Search "Establishment of minimum flight altitudes" ;)

[I-NNAV]

Hi FE
Thank you for your reply.
Are you talking about this doc (http://easa.europa.eu/system/files/dfu/Annex%20to%20ED%20Decision%202012-018-R.pdf)?
Because I didn't found where it talks about Net o Gross, but only about the separation requirements...
I'm really sorry guys, I'm usually good in finding this kind of info in the docs, but this time I'm stuck.
Maybe is just because Easa doesn't consider any difference between in flight and on ground planning, but I'd like to be sure...
Thanks!

[freekeer]

Hi I-NNAV,

Did you finally find the answer to your question?
I am struggling with exactly the same problem under EASA rules, and browsing the new AMC-CAT did not bring me any answer...

[FLX/MCT]

Gentlemen,

is this what you are looking for?

Commission Regulation (EU) No 965/2012
CAT.POL.A.215 En-route — one-engine-inoperative (OEI) (http://eur-lex.europa.eu/LexUriServ/LexUriServ.do?uri=OJ:L:2012:296:0001:0148:EN:PDF)
(a) The OEI en-route net flight path data shown in the AFM, appropriate to the meteorological conditions expected for the flight, shall allow demonstration of compliance with (b) or (c) at all points along the route. The net flight path shall have a positive gradient at 1 500 ft above the aerodrome where the landing is assumed to be made after engine failure. In meteorological conditions requiring the operation of ice protection systems, the effect of their use on the net flight path shall be taken into account.
(b) The gradient of the net flight path shall be positive at least 1 000 ft above all terrain and obstructions along the route within 9,3 km (5 NM) on either side of the intended track.
(c) The net flight path shall permit the aeroplane to continue flight from the cruising altitude to an aerodrome where a landing can be made in accordance with CAT.POL.A.225 or CAT.POL.A.230, as appropriate. The net flight path shall clear vertically, by at least 2 000 ft, all terrain and obstructions along the route within 9,3 km (5 NM) on either side of the intended track in accordance with the following:
(1) the engine is assumed to fail at the most critical point along the route;
(2) account is taken of the effects of winds on the flight path;
(3) fuel jettisoning is permitted to an extent consistent with reaching the aerodrome with the required fuel reserves, if a safe procedure is used; and
(4) the aerodrome where the aeroplane is assumed to land after engine failure shall meet the following criteria:
(i) the performance requirements at the expected landing mass are met; and
(ii) weather reports and/or forecasts and field condition reports indicate that a safe landing can be accomplished at the estimated time of landing.
(d) The operator shall increase the width margins of (b) and (c) to 18,5 km (10 NM) if the navigational accuracy does not meet at least required navigation performance 5 (RNP5).