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A320 FOM Vs FCOM Gear limiting speeds

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A320 FOM Vs FCOM Gear limiting speeds

Old 26th Apr 2018, 17:21
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C.M
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A320 FOM Vs FCOM Gear limiting speeds

I have a particular query with respect to the airbus limitations concerning the landing gear operating speeds.With reference to the picture attached , you can see on the left side ( which is the FCOM ) that the landing gear operating speeds , all 3 speeds have a Mach limitation (VLO : 0.67 , VLOextension : 0.60 , VLOretraction : 0.54 ) . When you look the section to the right which is the AFM , only the VLO has a Mach limitation . Is there a reason the AFM makes no mentioning of the limitation in terms of Mach ?This is important since the Mach limitations (basically the VLOextension) will be a consideration for extension in case of emergency descent from high altitude .
GEAR LIM. SPEEDS.jpg
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Old 26th Apr 2018, 21:01
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The OEM "shortest time to reach" EMERG DESC technique does not include L/G down.

The difference you see is most likely that:
- it was not flight-tested certified so it must not be in AFM
- people kept asking, thus Airbus calculated a value and wrote it in the FCOM.

The differences in legal meaning of AFM vs. FCOM vs. Company Approved Operating manual may differ across continents.

Last edited by FlightDetent; 8th May 2018 at 21:24.
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Old 27th Apr 2018, 03:57
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Originally Posted by FlightDetent View Post
The OEM "shortest time to reach" EMERG DESC technique does not include L/G down.
Maybe not as a part of the step by step procedure but...

"SPD: Max/appropiate. The landing gear may be extended. In this case speed must be reduced to Vlo/Vle"
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Old 1st May 2018, 19:36
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C.M
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Originally Posted by Escape Path View Post
Maybe not as a part of the step by step procedure but...

"SPD: Max/appropiate. The landing gear may be extended. In this case speed must be reduced to Vlo/Vle"
That’s one of the 2 points that prompted me to open the post . Is there a chance that airbus placed the Vlo/Vle to be respected also in terms of the Mach limitation?
Consider the emergency descent scenario with structural damage . In this occasion you would commence the descent in speed mode instead of Mach mode . If you are quite high (I.e over 35000ft ) and you decide to extend the gear to help in increasing your descent rate , if you respect the VLO_extension in terms of Mach (0.60) then you will have to reduce your speed significantly or wait to get quite lower ( it is at 25000 ft that the 0.60M will equate to 250kts ) . However if you respect the VLO_extention in terms of speed ( 250kt ) then your current cruise Mach will be already very close to 250 kt when you initiate the descent so you could extent the gear practically as you read the QRH.
So here comes the big question . Do we respect the AFM limitation which is only given in terms of speed ( and thus gives as greater flexibility) or the FCOM limitation which is also given in Mach ( thus restricts us at higher altitudes )
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Old 1st May 2018, 20:12
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Since there's a Mach limitation published in an approved manual, I'd respect both limitations. There used to be an altitude limitation for extending the landing gear which was removed, I reckon, because of the scenario you present. Since the Mach limitation is quite applicable to the scenario, I wouldn't bet against it.
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Old 8th May 2018, 09:32
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C.M
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To use the term “approved manual” is a bit tricky in this case. You were referring to the FCOM . It is not approved in the same sense the AFM is ( you can see that each documentary unit in the AFM has the “approved” next to it ) . The FCOM does not go through this process so it is not legally binding .
Another thing I noticed is that the landing gear placard speeds ( on the left side of the instrument panel) are as in the AFM. the only Mach limitation you see on the placard speeds is as it is in the AFM ( only the VLE)
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