Non etops 60 min range

[tuaapache]

Hi all,
I have a question regarding the radius to fly for 60 minutes based on diversion speed for 737ng.
Let’s say we have an engine failure at 35000 feet and we drift down based on the engine out speed from engine out page in the fmc as soon as we reach the level off altitude for one engine, we would look at the long range cruise Table for one engine in the fcom, would this be the speed to fly for one hour and also the radius in 60 minutes. Let’s say LRC is 250knots , so the radius would be 250 nm. What am I missing here?
Cheers

[FlightDetent]

Not much, IAS to TAS conversion perhaps. What is the question?

Be aware, though, that the 60 minutes rule is merely a calculation in the planning stage. It is a compliance exercise.

The connection to what the pilot needs to do in case of an engine failure is remote if any at all. There is a set of rules what needs to be done, but those have roots outside this 60 minutes planning restriction.

At this point I will on purpose not tell what the 60 minutes rule actually tell us, because rephrasing the original legal text only leads to ambiguity. It is written the way it is, meaning precisely what it says.

If you look it up and paste here with a reference, we can go word by word and clarify as required.

[tuaapache]

my question is what would be the speed(ias tas Mach or groundspeed) or the correct way to find the speed in order to find the radius that we can fly for 60 mins. I am aware that the speed is non linear due to weight, so the speed varies day to day. I thought that the diversion speed can be tas ias or mach but normally Mach/ias is used rather than tas based on icao.

[FlightDetent]

The "60 minute rule" is a misleading name. It is a distance rule, that you already understand. I re-iterate: to be used in the planning phase, not in flight.

Usually, in a galaxy far, far away .....

This distance must be approved by the relevant CAA, and then written into the operating manual of the AOC holder. Therefore before approving a new type for the airline, the Flight Ops Engineering will have a look into the LRC tables you mentioned. Let's say they find 250 kt IAS per your example above which translates to 398 kts TAS for the LRC ceiling.

Then the AOC holder would go to CAA and request approval for "60 minute rule" planning permission with the range of 398 miles. The CAA will look at the tables and say: "No, we have a different opinion, you have calculated the TAS incorrectly. Try again and
- use MTOW instead of MLW for weight
- use values for ENG anti-ice on, instead of no anti-ice at all
- use values for most forward CG, instead of 30%
- use values for ISA+20, instead of ISA
- ... etc."

and the number is 361 kt TAS = 361 NM.

Meanwhile your airline finds out that the competitor - the flag carrier of the country who fly the same aircraft - have approval for 380 kts. So your boss will ask the investors in your company to contact the government officer responsible for overseeing the CAA and seek understanding, that we need to have a level playing field.

Then your Flight Ops engineers will calculate LRC TAS for
- MTOW minus 4000 kg (one hour away after take-off)
- ISA +10 (average temp in the region at LRC OEI ceiling)
- engine anti-ice on
- normal CG 30%

and the number is 387 kt TAS = 387 NM

You go to the CAA the second time, bring the calculations expert along. Once they listen to the technical reasoning, shaking their heads in all directions looking serious and important, it is time to stand and say: "For the interest of flight safety, we wish not operate extremely nor dangerously. To make sure the travelling public is always in the best hands, we ask the almighty CAA to allow only 380 NM, always on the conservative side!!!"

Then you hand over the written request. Behind the last page of the submission, by an unfortunate mistake, there is a loose copy from the national airline's manual where the 380 NM distance is written. Which is completely not relevant at all.

After 30 days you receive the letter of approval for 380 kt = 380 NM; it is written into your manuals and becomes the rule.

Here is the answer for your question: The distance is NM is defined by LRC TAS in still air. Before dispatching a flight, colleagues from the Flight Planning Department would find this number in the operating manual. It is a fixed value distance, approved by the national CAA. They will create a route inside 380 NM range from adequate airports.

For the pilot with a failed engine, none of the above matters. He/She will follow the OEI drill, fly the best speed and altitude profile appropriate to the situation, aiming to land at the nearest available airport (in the terms of time).

--------------

The story is a purely fictional illustration that the "60 minute rule" distance is only an arbitrary number. Based on some universal traits of human nature observable around our little globe.

For the record, I have both heard and experienced dealings with CAA(s) that were much easier and conducted in a helpful manner with keen interest to get things right without willy-waving.

[tuaapache]

Thank you so much for your reply. Just curious how would i convert ias to tas? Is there a table that i can use to convert ias to tas?
Cheers

[FlightDetent]

:) Is 42 the solution? Does Google exist? Was POTUS American born? Is 737 FBW? How late is my salary this month?

...so many questions...:{

[rudestuff]

Thank you so much for your reply. Just curious how would i convert ias to tas? Is there a table that i can use to convert ias to tas?
Cheers
Ask your PPL instructor to show you a flight computer

[swh]

my question is what would be the speed(ias tas Mach or groundspeed) or the correct way to find the speed in order to find the radius that we can fly for 60 mins. I am aware that the speed is non linear due to weight, so the speed varies day to day. I thought that the diversion speed can be tas ias or mach but normally Mach/ias is used rather than tas based on icao.

The speed is whatever is written on the table in the FCOM. often this is MMo/Vmo or Vmo-10.

The rule distance for the airline is normally the worst case scenario for the airlines route network assuming maximum weight the aircraft could expect on the relevant route in its network (which maybe MTOW/MLW/MZFW limited).

Different airlines can have different rule distance fir the same type.

The speeds flown on the day is entirely the pilots decision, they are not required to fly the speeds the rule distance table is based on or to land within 60 minutes.

[FlightDetent]

That is an important correction. The speed for the "60 minutes rule" comes from the PERF section of the airplane manual. But you are allowed to pick any realistic one, and then apply with the CAA to have it authorized.

That is of utmost importance for LROPS A/C, where a very high OEI speed is desirable to increase the range circles for crossing uninhabited territories. At the cost of the extra/additional fuel expense where required.