En-route One engine inoperative

[Dollehz]

Hello,

Quick question concerning the interpretation of this paragraph from the EU-OPS:

EU-ops 1.500 En-route - one engine inoperative

...
at all points along the route. The net flight path must have a positive gradient at 1 500 ft above the aerodrome where the landing is assumed to be made after engine failure
...
The gradient of the net flight path must be positive at at least 1 000 ft above all terrain and obstructions along the route
...
The net flight path must permit the aeroplane to continue flight from the cruising altitude to an aerodrome where a landing can be made ... the net flight path clearing vertically, by at least 2 000 ft all terrain and obstructions along the route
...



My interpretation: is that you must have 2000ft obstacle clearance.
During climb (positive gradient) obstacle clearance can be reduced to 1000ft.
1500ft above alternate the aircraft must be able to climb.

Most common interpretation: 2000ft obstacle clearance during driftdown, then 1000 ft.
1500ft above alternate the aircraft must be able to climb.

Which one is correct?

Thanks

[sonicbum]

Hi Dollehz,

If you loose an engine and according to the performance of the airplane you can't clear all terrain and obstructions along the route within 5 NM then you must ensure that your plan B (escape route or contingency route) clears the obstacles by 2000 ft with a negative gradient again within 5 NM of the intended track. Example if you fly over the Himalayas most of the twins won't be able to cope with the 1000 ft positive gradient (some segments have a route MORA of 29000 ft) so if you loose an engine there you need a back up plan, that is a routing that will cover you and get you on the ground within the required 2000 ft with a negative gradient. You will have a negative gradient obviously till you reach your single engine drift down ceiling.
Hope that makes sense.

[Dollehz]

Hello Sonicbum

Thanks for your reply.

What you say makes perfect sense but its still not clear to me which of my 2 given interpretations are correct.

When talking about the 1000ft obstacle clearance, a positive net gradient is required.

Does this mean that:

a) obstacle clearance is 1000 ft when climbing
b) obstacle clearance can be reduced to 1000 ft if the aircraft is capable of climbing (but not necessarily doing so)

To my understanding:

When an engine fails and cruise altitude can not be maintained, you have do descent, with 2000 ft obsacle clearance. Then when reaching the driftdown altitude minimum obstacle clearance is 1000ft? 2000ft?
For the 1500ft: this is just a requirement limiting available options in diversion aerodrome (elevation)

This may be the cause of my confusion: Does the driftdown altitude assures you a positive climb gradient or is this the highest possible altitude the aircraft can maintain (level flight)?

[john_tullamarine]

Consider looking at things simply -

(a) the aim of heavy aircraft certification is to permit the aircraft to suffer a major failing and the crew still be able to recover to a safe landing

(b) it follows that, en-route, an engine failure (or shutdown) ought not to result either in the aircraft's falling out of the sky or getting up close and personal with the rocky bits.

(c) therefore, in the event of that failure (or shutdown) either -

(i) you can continue with a minimum terrain clearance (capability) of 1000ft (positive gradient capability just means that you can avoid going down) OR, if you can't do that, then

(ii) you can put your pre-determined descent plan into action while maintaining a minimum of 2000ft terrain clearance on the way down. It may be that you combine the two options and descend to a lower level where you are able to continue level flight

Note that the capability of the aircraft for this purpose is as specified in the relevant section of the AFM and will include some fudge factors not necessarily disclosed to the pilot.

Does this mean that:

a) obstacle clearance is 1000 ft when climbing

As a capability, the aircraft needs to be able to maintain level flight OEI with 1000ft minimum terrain clearance throughout the en-route stages of the flight OR the subsequent flight MUST be predicated on the descent and 2000ft strategy until level flight can be maintained. So one would apply this for climb, cruise and descent. In practice, for most situations, this means we look at the cruise situation.

b) obstacle clearance can be reduced to 1000 ft if the aircraft is capable of climbing (but not necessarily doing so)

The capability is to maintain level flight per the AFM data (which actually would permit a rather modest climb). It's one or the other - level flight with 1000ft clearance OR descent with 2000ft min clearance either until you are in the approach and landing phase or can maintain level flight. One presumes that, if you are concerned with real terrain clearance in level flight, you really aren't considering descending ..

As a silly example, I used to look after some Argosies (Britain's Queen of the Skies). The original AFM which came with the aircraft didn't have OEI cruise data .. so the Regulator applied some undesired operational restrictions ... and we had to jump through the hoops to modify the AFM to include suitable data. Actually, I guess that wasn't too bad as I got paid to do the work ...

Then when reaching the driftdown altitude minimum obstacle clearance is 1000ft? 2000ft?

1000ft

For the 1500ft: this is just a requirement limiting available options in diversion aerodrome (elevation)

Think of things in a slightly different way .. you really don't want to make it a forced landing from 35,000 ft .. while the Shuttle pilots no doubt derived a buzz from doing that from a far greater height, we mere mortals prefer flying a circuit ... ergo, let's give ourselves some capability for flying an OEI circuit before we end up placing the wee beastie delicately onto the runway ...

Does the driftdown altitude assures you a positive climb gradient or is this the highest possible altitude the aircraft can maintain (level flight)?

Same thing. Positive gradient just means you can stop going downhill.

[Dollehz]

Wow thanks for the amazing reply!

Covers all my questions! :)

Although i'm sure you know what you are talking about, i cant find anything official on positive climb gradient being equal to level flight nor does the EU-ops speak of positive gradient capability

It literally says :

The gradient of the net flight path must be positive at at least 1 000 ft above all terrain and obstructions along the route

Don't take this the wrong way, i love your reply.
I'm just a 'I-need-to-see-it-in-an-official-document' type.. :8

[john_tullamarine]

i cant find anything official on positive climb gradient being equal to level

Nor do I expect that you would.

Simple definition interpretation - positive means anything better than zero so, in the limit, it means not worse than just a poofteenth better than zero .. ie, in effect, zero. The AFM data has margins built in .. leave you to dig out the specific numbers in the regs if you want ie, at the AFM ceiling you will have a small capability to climb but not much.

nor does the EU-ops speak of positive gradient capability

I'm not an EU man so I'd have to do some digging to check out the rules over there in detail. However, anything to do with certification gradients relates to an aircraft capability .. what you might do with such a capability is up to you and the operational rules to which you may be subject.

The gradient of the net flight path must be positive at at least 1 000 ft above all terrain and obstructions along the route

Precisely .. and that is a capability which the aircraft must possess providing the weight is selected/constrained appropriately

I'm just a 'I-need-to-see-it-in-an-official-document' type

Unfortunately, I think you might have to remain dissatisfied this time around. Having said that you might like to research some of the EASA compliance certification or FT guidance material .. you might find something to your liking there ..

[Dollehz]

After further research I found this in a FCOM:

A detailed study of each route over mountainous area must show that single-engine net flight path and passenger oxygen system performance allow the aircraft to clear the obstacles by 1 000 ft in climb and by 2 000 ft in cruise or descent. If the aircraft in these circumstances cannot clear the obstacles on the route, a PNR must be determined and diversion procedures must be established.

:confused::confused::confused::confused::confused:

[john_tullamarine]

(a) FCOM words do not a regulation make ...

(b) perhaps engage the FCOM OEM tech folk and ask the question "whence comes this advice ... ?"

[Dollehz]

Unfortunately I don't have access to those guys :(

The FCOM just adds up to the confusion.

Anyway I guess you are right John, your explanation makes perfect sense to me.

Thank you very much for your time! :ok:

[john_tullamarine]

Doesn't matter who they are .. either

(a) if it's your employer's Type .. go through your CP

(b) otherwise, run a search, find a contact at the relevant OEM, and then ask the question.

Plenty of folk here have personal interaction with OEMs .. no reason why you shouldn't try.