Help one hour single engine 737 calculation

[BEASTPLOTINTHEWORD]

Hi folks!
As a new Boeing 737 300 pilot I am having some trouble in calculating exactly how many miles we can cover in one hour to the takeoff alternate if we lose one engine.

The QRH doesn't help much, it covers the cruise engine failure.

Any help would be apreciated.

Thankyou.

[Rainboe]

For practical purposes, BA used 400 nms.

[Old Smokey]

Most regulatory authorities (but I cannot speak for all) consider that the 1 hour requirement is satisfied by using the distance approved as 60 minutes from a suitable airport for ETOPS planning.

The "60 minute radius" for the B777 ETOPS calculation in our AOC is 432 nm, and for the purposes of considering the "Departure Alternate", a suitable airport within 432 nm is considered acceptable, even though the actual flying time might exceed 1 hour.

Seems a good practical approach to me.

Regards,

Old Smokey

[LEM]

It really varies with conditions, the weight, the obstacles enroute thus the cruise altitude to be reached...

Yes it's not that easy to calculate exactly the amount of miles you can cover in exactly 60 minutes if you lose an engine at rotation.

We are not provided with any info about the climb rate in single engine, and it varies a lot with weight.

Let's assume a 1000 foot rate after cleanup.
Let's also assume a cruise altitude of 10000feet.

It's gonna take 10 minutes to reach 10000ft at 210 knots.
This covers about 40 miles.

Then I would use the Long Range Cruise Control table of the QRH, ENGINE INOP, of course.

For a 50 tons (I've got the 400 22k table, but roughly it's the same for the 300) weight, at 10000ft it gives a speed of 279 kts, or . 5 mach.

5 miles a minute.

After our climb we are left with 50 minutes.
50 minutes at 5 miles a minute, makes 250 miles.

Take something for the slower approach speed, add the 40 miles covered in climb, and the result is...


280 miles.

And we have a winner!!!!!!!!!!! :}

LEM

[Dehavillanddriver]

LEM,
Sorry old chap, but you have missed the point of the calculation completely.
The point of the exercise is to get the BIGGEST single engine circle that you can - it is quite a complex calculation if you do it properly, involving take off at max weight, climb to max practical cruise altitude for the weight, cruise for a period of time, have an engine failure, descend to a single engine cruising altitude etc etc (from my distant memory!)
Old Smokey gave his company's number - 432 nm.
In our company it depends on engine, airframe and winglet configuration but varies around 410-430nm (roughly).
By using the calculation methods that you used you limit yourself to using airports within your 280 nm range ring, which in practical terms is quite limiting.

edited to change depressurise to have an engine failure - thinking about something else at the time!!

[LEM]

Just to avoid any misunderstanding, I think BEAST asked about the distance we can cover after an engine failure at takeoff, not in cruise.

There's quite a difference.

I think you guys are a bit optimistic, as the whole climb will be done at minimum clean, 210-230 kts for a 737 300.

Then the cruise speeds apply...



Dehavillanddriver,
If I have missed it completely, as you say, you teach me please!

As I stated in the beginning, it varies a lot with conditions.

Mine was a pure example.

Show me how to do it.

Btw, cruise for a period of time, depressurise, descend to a single engine cruising altitude etc etc , shows maybe the one who has missed it completely is not me...:confused: :confused: :confused:

LEM

[widgeon]

This is probably a stupid question but what are the circumstances that prevent you going around and landing at the same airport in the event of an engine failure ?

[AerocatS2A]

This is probably a stupid question but what are the circumstances that prevent you going around and landing at the same airport in the event of an engine failure ?

Bits of your engine scattered smouldering on the runway?

[Empty Cruise]

T/O in 125 m. RVR - one engine fails - now Cat I limited - 550m - minus 125m = doh! :}

Just a suggestion

[mutt]

ETOPS calculations are based upon starting at your optimum altitude and drifting down, the TAS is therefore a high value and isn’t representative of the flight profile associated with a departure alternate. I therefore believe that LEM’s answer is the correct one!

Mutt

[BOAC]

I would not begin to challenge Lem's figures, Mutt, but I suspect from the way the 'q' was worded that (as LEM says) it was about the figure for the take-off alternate calculation requirement in JAROPS which, as I said, was 330nm in BA for the Classic and typically 340nm for a NG.
For this 'reality'/ETOPS considerations do NOT come into it:)

I deleted my first post which was getting well into complicated territory, and would agree that the 'beast' IS just after the distance for the take-off alternate.

This is based (in JAROPS) on the AFM declared 'single-engined cruise speed' and is used purely for PLANNING the alternate. It has very little to do with how far you would actually go in one hour, which is probably close to Lem's figure. I.E. In reality if you flew for 1 hour after take-off, engine out and only got 280 miles in that time towards your nominated (and 'legal') t/off alternate 330 nm away, you would obviously keep going until you get there.:)

[Capt Chambo]

If you are a JAR operator then there should be a value published in your Operations Manual, part B.
Various operators manage to get varying distances approved, the one I have to hand at the moment shows 330nm, and is roughly consistent with other B737-300 operators I have flown for.
Personally I would use the value published by your company, before trying to calculate something of your own.
Enjoy the aeroplane it can be fun!

[Dehavillanddriver]

LEM, perhaps I read too much into the question, but I assumed that beast was asking about takeoff alternates.

In Australia you must if the departure aerodrome is closed for arrivals (i.e.fog) you must provide for an alternate within 60 minutes.
For the purposes of the Australian calculations (which I accept is not necessarily the country that Beast was asking about) the "60 minutes" is determined using the calculation that determines the 60 minutes speed/range for ETOPS. The logic being that 60 minutes is 60 minutes regardless of whether it is ETOPS or not.

So this all being the case the aim is to get as big a distance as possible to maximise the operational possibilities, in some cases you may not have an airport within 280 nm and in some cases this may prevent you from departing. The bigger the distance the more potential airports that can be used as a takeoff alternate.

To do this the calculation as others have said is quite complicated and needs to be done and published in an ops manual, not done on the day, which means that it does NOT vary with the conditions. Remember this is a number for planning purposes and may bear no relation to what you may fly on the day.

If it DID vary with the day, you may have a situation where you could depart on one day and carry airport X as a takeoff alternate, but on the next day, because the aeroplane is heavier or whatever, you may not be able to depart carrying exactly the same airport.

Logically having 2 figures for 60 mins S/E (i.e. an ETOPS figure and a NON-ETOPS figure) doesn't make sense to me because a flight is either ETOPS or not. If it is not it has aerodromes within 60 minutes - if that makes sense...


Let's assume a 1000 foot rate after cleanup.
Let's also assume a cruise altitude of 10000feet.


LEM - I don't think that you would cruise a 737 at 10000', around the mid 20's perhaps.

[LEM]

I perfectly agree this is a planning figure.

I didn't know this figure is fixed and has to be certified.

In my company manuals it's not published, while I recall it was in another company, but on a different airplane.
Now I know it should be published under Jarops, thanks to your input.

Re: the 10000ft in my example: I know this is too low, but I deliberately choose this figure in order to be able to accelerate as soon as possible, so to obtain the longest distance flown.
Like you, I wouldn't really care if it took one hour or something more to get to the takeoff alternate.
My concern was only to defend my selection of the alternate before a judge...

Since you tell me the certified distance is 330 miles, fine, I'll take 330 from now on.
Good to always learn something.

:ok: LEM


Ps: the Beast in fact was asking about "... the takeoff alternate...", so no doubt he got his answer by now.

[BOAC]

Since you tell me the certified distance is 330 miles, fine, I'll take 330 from now on- not quite what I said!as I said, was 330nm in BA for the Classic -so be wary and check with your AOC!Ps: the Beast in fact was asking about "... the takeoff alternate...", so no doubt he got his answer by now- I would hope that was it?

[B737MRG]

Hi,

if I read my manual, it says "... a takeoff alternate is available within a range of 1hr flying time at single engine cruising speed based on the actual takeoff weight, still air and standard conditions."

I stand to be corrected (I consulted some colleagues), but this means that "1hr" is only a value to calculate the range, while it is not a "time limit".

If your FPPM says your single-engine ground speed is 300 kts for the given weight, you can take an aerodrome located 300 NM from your departure airfield as your takeoff alternate. And you will not reach this alternate within 1hr, since your speed during climb and descent/approach will be less.

If your OM doesn't state any specific company value (range), the procedure would be :

- take the TOW
- take the cruising flight level you will fly to clear terrain
- refer to the One Engine INOP LRC table in the FPPM to obtain the single engine cruising speed
- multiply speed (kts) by 1 hour = distance/range (NM)

Perhaps I am wrong, just let me know,

Pat

[Old Smokey]

Well, we've gone full circle on this one, and B737MRG managed to complete the loop quite nicely with the statement "a range of 1hr flying time at single engine cruising speed". Yes, there are many more complex ways of calculating a Climb / Cruise / Descent profile to be contained within 1 hour, but it must be remembered that it is to satisfy a legal requirement, not an operational one.

I cannot speak for all Regulatoty Authoritys, but the SPIRIT of the legislation is akin to the ETOPS requirement, i.e. the radius of action is based upon Cruise speed OEI, not the complete Climb / Cruise / Descent profile.

Regards,

Old Smokey

[Blip]

Here's a question for you. (Especially B737's)

If your destination happens to also be your One Engine Inoperative or Depressurisation Alternate, how are you going to demonstrate during the flight planning stage that you have enough fuel to arrive with the required reserves in the tank?

This question assumes that you want to dispatch with the minimum "Normal" fuel required. How do you know this figure doesn't require a "contingency fuel" top up??

[Jonty]

This relates to B757, but we use 400nm as the distance. This means we can use any airfield as a departure alternate as long as its within 400nm of our departure airfield, as long as it satisfies all the other criteria. This distance is also the declared distance in the Vol1.

As LEM said though, it would be interesting to see if you could fly 400nm in one hour after a cut at V1

[BEASTPLOTINTHEWORD]

Tkanks everyone for help.
Very interesting discussion.

:ok: