Boeing 737 Maximum Operational Latitude

[QJB]

Hi all,

Just curious,

I had a look at a Boeing 737 FCOM on the net and in the operational limitations section I found the following:

MAXIMUM FLIGHT OPERATIONAL LATITUDE: 73 NORTH 60 SOUTH

Can someone shed some light on why this limitation exists. Sorry if the answer is obvious.

Cheers,

J

[singpilot]

It's not obvious. Flight limitation is derived from IRS platform limitations AND flight test verified performance. It's what someone (with the need) paid for.

IRS/FMS initialzation latitude limitations may be different as well.

[Rainboe]

Because the IRSs will have trouble aligning with sufficient accuracy. They rely on sensing Earth rotation and establishing latitude. The nearer you get to the Poles, the more of a problem it becomes. If you consider a horizontal gyroscope at the equator, it will very quickly sense a tipping force as the Earth rotates. At the Poles, the tipping force will not be there, the Earth's rotation will be masked by the motion of the gyroscope wheel itself. But quite why the latitude limits are not the same North/South I have never understood, but they have designed the system to work at all likely terminals!

[Intruder]

The actual limit is 90 degrees. The 60 degree stated limit gives the obligatory 50% margin. They must have a waiver for 73 degrees... ;)

[jcbmack]

QJB,
please see here from another PPRUNE thread: http://www.pprune.org/questions/107831-flying-over-poles.html

Some routes will actually go very near or over the poles, as FlyingForFun pointed out, and there is further information from the ATPL theory exams.

As one approaches the North Pole,the heading may change very quickly; please see here pp. 3-4: http://www.freelancepilot.nl/ATPL%20summary.pdf

There also needs to be a fuel-freeze strategy and monitoring for North Pole operations.

Pay special attention to Glueball's post from the thread I linked to you, but please read all posts.:ok: He really thoroughly offers a full treatment to the question at hand.
I give credit to all those posters from Flying over the poles started Nov 2003 for providing far better explanations than I.:}

Please see here:Emirates A330 Flies Over The North Pole! — Civil Aviation Forum | Airliners.net (http://www.airliners.net/aviation-forums/general_aviation/read.main/468554/) Interesting related flight occurrence over the NP.

[jcbmack]

Just as a follow up, also consider what complications might arise in lieu of violent weather conditions, not only on flying over the NP, but also in landing, the period of time on the ground, take offs, and evacuation procedures should issues arise on the spot.

[Spooky 2]

All current B737NG aircraft are certified for Polar Ops with certain limitations. You did not specify what model of 737 you were referencing?
As for initialization of the FMS it is simply a matter of where and how the certification took place. I do not have the 737 data at hand but in the case of the 777, the highest latitude that the airplane ADIRU can be initialized corressponds to the airport Lat. at Svalbard (Longyearbyen-EBSB), which just happens to N78.14.75 minutes. I would bet that the 737NG is the same as the BBJ's are capable of some Polar flight plans

The FAA has defined Polar Operation to begin above N78. Generally speaking there is no "violent weather patterns in the Polar regions. Snow and whiteouts, yes but the area is some devoid of the weather systems that can be found at lower latitudes. Operators need special authorization to operated in the Polar regions and that would include familiarity with communication issues, passenger recovery, alternates, QFE/Metric altimeter procedures, MNPS, solar storms, HF blackouts, ETOPS, etc. The list goes on and on.

[FCS Explorer]

Maximum flight operating latitude - 82° North and 82° South, except for the region between 80° West and 130° West longitude, the maximum flight operating latitude is 70° North, and the region between 120° East and 160° East longitude, the maximum flight operating latitude is 60° South.

and

Air Data Inertial Reference Unit (ADIRU)
ADIRU alignment must not be attempted at latitudes greater than 78 degrees
15 minutes.

[CaptainSandL]

73N & 60S are the 737CL limits, the current 737NG limits are as stated by FCS Explorer. Unless you have the polar option in which case there are no limits. The polar option includes a Heading Reference switch on the aft overhead panel which allows crew to switch between magnetic and true on all displays.

[jcbmack]

Here:
737-600/-700/-800/-900.
The primary roll mode for polar operations should be LNAV. The heading reference switch must be in the TRUE position to enable flight control computer engagement, HDG SEL mode, ROLL CWS mode, and heading display on the RMI. Deviations from the planned route may be accomplished in HDG SEL mode.
http://www.boeing.com/commercial/aeromagazine/aero_16/images/polar_sidebar2_737.jpg















http://www.boeing.com/commercial/aeromagazine/aero_14/images/top_of_page.gif (http://www.boeing.com/commercial/aeromagazine/aero_16/polar_nav_by_model.html#top)
Differences between the heading display on the PFD/ND and the RMI may exist within approximately 30 nmi of a pole because of differences between the FMC position and IRS position. For GPS-equipped airplanes, loss of both GPS units results in an increased ANP and possible display of the UNABLE REQD NAV PERF-RNP annunciation, but this normally would not prevent polar operation.
Loss of one IRU does not significantly affect navigation accuracy. Operation on the remaining IRU should be limited to diversion to the nearest suitable airport.
In the event of dual IRU failure, the left GPS true track is displayed on page 3 of the PROGRESS pages on the CDU. This serves as a tertiary backup for the airplane heading or track and an update to IRS ATT mode.
Polar navigation option.
These latitude limitations on flight operation do not apply to 747-400, 777, and 737-600/-700/-800/-900 airplanes equipped with the polar navigation option (heading reference switch and FMC Update U10.3 or later) and dispatched with the following equipment operational: CDU, left GPS, both IRUs in navigation (NAV) mode, and both display electronic units.
Flight crews of such equipped airplanes should not use HDG SEL or ROLL CWS north of 89 deg 30 min north latitude or south of 89 deg 30 min south latitude. They also should not use the heads-up display system, if installed, when the heading reference switch is in TRUE.


Aero 16 - Polar Route Navigation By Model (http://www.boeing.com/commercial/aeromagazine/aero_16/polar_nav_by_model.html)

The flight/nav specifications vary by model and year. As 737's and navigation techniques in general, improve, more can be done by way of polar flight.:\

[jcbmack]

A thorough review of operation specifications would not hurt; perhaps a separate thread for this as well?:}

Found this in my reading: http://www.pprune.org/tech-log/320697-rnp-rnav.html (for contrast).

[Spooky 2]

Opspecs B055 covers Polar Ops. The best source of information for this issue is AC120-42B, Chapt. 6, which was written after the Polar Ops article published by Boeing. Also requires B040, Ops in the NCA/AMU as a part of the application process.

Operations in the Polar region typically require a validation flight by the FAA. Since there are very few Nav Specialists in the FAA (maybe less than 4), you need to get name on the list well in advance.

[jcbmack]

:ok:...thank you Spooky!

[QJB]

Thanks everyone for taking the time and effort in replying.

J

[DPTG]

Actually,the B737 IRS can align up to (and down to) 78*15' N and S (by the special procedure for the high Lattitude alignment begin from 70*12' to 78*15' (~17 mins)) because it affected by the earth rotation force alone,but for some reasons that we require to convert the result from the IRU such as the true heading and so many things into the magnatic reference when we fly. So we require the MAG VAR data to convert those things which is become the limitation of the B737 CL because they have the internal MAG VAR data for B737 IRU only from 73*N down to 60*S.
Regards,
KANIT A.:)

[Firestorm]

A quick look at my school boy atlas reveals what may be interpreted as American Imperialism. The latitudes quoted approximate to the Northern coast of Alaska, and just beyond the Southern tip of South America.

[Spooky 2]

For alignment limitation purposes Boeing uses Longyearbyen (Svalbard) ENSB. This airport is 78.14.46N / 152.27.56E, thus this is the limitation imposed on most if not all Boeing airplanes regarding the alignment process.

[standardset]

Apart from Antartic bases there are no airfields further south.

[Yaqatari]

For the 737-700 it is 82* north and south except for between 80 & 130* west it is 70* north and between 120 & 160 east it is 60 south.

Regards

[THR RED ACC]

You really do have to ask yourself..

why would a 737 need to go that far north/south anyway?