90 Minute Rule 3/4 Jet

[Oxford1G]

Could anyone explain where the 90 minute rule for the 3 and 4 engine operations came from, as this could be quite restrictive on the North Atlantic etc ?

Thanks

[static]

What 90 minute rule?
At least for 4 engined aircraft I know of no limitations for distance to enroute airports, for instance.
Please explain further.

[Oxford1G]

JAR OPS, now require that 3 and 4 engine aircraft have to consider a double engine failure if operating more than 90 mins at an all engine TAS.ie all engine TAS of 460kts equals a distance of 690nm.

[411A]

More "fuzzy thinking" on the part of the JAR crowd :rolleyes:

[Check-in]

When you say "consider" does it mean for the purposes of drift down and range, or is it a restriction on maximum distance at the planning stage? If only for drift down (ie terrain clearance) and range, seems it would not be all that restrictive for four engine
types. Depressurized case would be more limiting anyway? Don't have access to the JARs, so am asking, not suggesting.

[4dogs]

Folks,

There is nothing new in the 90 minute rule - it is of the same vintage as the 60 minute rule for twins and comes from the ICAO performance deliberations of around 1953. It is in FAR 121 and, for ozmates, CAO 20.7.1B:13 something.

It is tied up with two engine inoperative performance - if you can maintain LSALT for the route sector on one (3-holer) or two (4-holer) then it is not applicable. Presumably, most of the North Atlantic has low LSALTs and hence the rule is not limiting. If you want to play in the Andes or the Himalayas (or Indonesia), then it is a different ballgame.

From memory, driftdown is part of the calculation. Similarly (memory, that is), I cannot remember any regulatory relief for the 90 minute rule to parallel the ETOPS relief from the 60 minute rule.

------------------
Stay Alive,

[email protected]

[xyz_pilot]

So 411A would you like to explain why this is such a bad rule.

Or is it your normal talk first think second act.

[This message has been edited by xyz_pilot (edited 31 December 2000).]

[411A]

Restrictions on 3 or 4 engine aircraft are few and has been pointed out above have to do with driftdown and MSA. However the JAR crowd have a propensity to over-regulate as for example, their recent proposal (now abandoned) to employ ETOPS rules for private two engine business jets. Now lets see, how many two engine business jets or 3 or 4 engine jet aircraft have gone swimming in the North Atlantic in the last 25 years? Only one that I can recall, a B727 that ran out of fuel due to poor planning on the part of the flight crew. The JAR crowd seems to think that...."if it ain't broke, lets fix it anyway". As I said, fuzzy thinking :rolleyes:

[RoboAlbert.on.his hols]

When I flew the older C130s now in RAF service we would often need to consider the 90 mins rule (which equates to an embarrassingly small distance at our TAS!). Quite commonly if crossing the Atlantic on a northerly track, over Greenland, we'd have a problem with our 2 Eng Stab v route S Alt. Although its rare I'll admit, people have lost 2 in the cruise so I think it’s probably something to think about....

...or we could just operate to 411A's 'hope for the best' regulations.

xyz_pilot if you want the answer to your question, try a search for his other posts it's classic stuff.


[This message has been edited by RoboAlbert.on.his hols (edited 01 January 2001).]

[This message has been edited by RoboAlbert.on.his hols (edited 01 January 2001).]

[411A]

The rules come from the US FAA, but of course for the JAR crowd, these are not good enough. Glad to see that, as this will only drive up the costs for European operators to make them even MORE non-competitive. More gravy indeed for US airlines :)

[RoboAlbert.on.his hols]

More lucid, consistent and compelling arguments 411A. Just a couple of questions...

- How come we’re claiming these rules for the good ol’ FAA? Were they not formally the products of the JAA’s fuzzy thinking? Actually neither, as 4dogs pointed out.

- Both sets of regulations (FAR121.193 and JAR-OPS 1.505) would seem to be in broad agreement. The only superficial difference is that the JAA’s wording highlights the need to consider the use of anti-icing systems. FAR 121.193, although only including a mention of ambient temperature, would also require the operator to consider whether the anti-icing systems would be in use, since this would form the basis of any meaningful calculation of net flight path data. How then do the two sets of regulations differ in any material respect?

I look forward to you thought provoking reply (and further culinary banter)......


PS On my hols I have tried American gravy – it is poor stuff, a thick paste of flour and fat. I fear that the US is not ready for our fine European gravy.

[411A]

The US regulations address net flight path data and performance, and rightly so. However, it is my understanding the the JAR crowd is proposing a mandate for a 90 minute enroute alternate. This would be impossible, for example, on many routes in the Pacific.
This 90 minute rule would be a good idea for turbo-propellor powered aircraft but really not necessary for turbojet aircraft provided they could meet the drift-down requirements. As I mentioned before, it would appear that the JAR's have a solution looking for a problem which does not exist.