View Full Version : waypoint in leu of navaid

26th Jul 2011, 07:33
can we use an fms waypoint in leu of an inop approach or departure navaid?

26th Jul 2011, 11:42
Don't have a reference, but I'm pretty sure the following applies:

If the approach or departure is non-rnav, i.e based on conventional navaids, then they must be operating as intended for the approach. For example, if the approach is an VOR/DME, you must have both VOR and DME indications, unless specific timing is given in the case of an inop DME.

Likewise for departure. if it is based on conventional navaids, then you must be able to use them. I know most people simply select LNAV once airborne irrespective of whether it is conventional or not, but as far as I'm aware, you must still be able to used the navaids defined in the procedure.

Border Reiver
26th Jul 2011, 12:35
That is I believe correct. You can opt to fly the approach in managed mode if all requirements are met but one of those will be displaying the nav aids related to the approach.

26th Jul 2011, 18:51
I dare to say that you can use it as long as you have rnav 5 or better which I am sure any fms meets.

27th Jul 2011, 11:12
Hi MD83FO,
can we use an fms waypoint in leu of an inop approach or departure navaid? It depends:

On departure, if you can confidently climb above SSA/MSA without the benefit of the radio aid, then it's OK. Some departure charts will specify what aids need to be available, e.g. FMS + GNS, DME/DME.

When descending below MSA/SSA, you can't substitute an inoperative approach aid with a(n) fms waypoint, so you'll need the published approach aids to be working. There may be a GNSS app published (e.g. LGW).

27th Jul 2011, 11:59
I dare to say that you can use it as long as you have rnav 5 or better which I am sure any fms meets

RNAV 5 for approach and dep??? :=

This is copied from our ops manual:

The operational requirements and procedures are determined by the type of RNP route
or airspace, and will differ for :

Type of RNP Route or Airspace ----> RNP/GPS Capability
En-route, oceanic (Atlantic / Pacific), or remote areas ---> 10
En-route or terminal area within radio navaid coverage ---> 5 / 4
SID/STAR based on RNP ---> 1
RNAV approach based on RNP---> 0.3

27th Jul 2011, 12:44
if the radio aid is u/s it will not affect the FMS, and the procedure will be perfectly flown by the FMS.

Edit. deleted remark.

"The Navigation Database must be current.
– The approach is stored in the navigation database
– GPS will be used as the navigation sensor for “Overlay” approaches.
– Conventional aids must be displayed."

27th Jul 2011, 13:11
I interpret the question as

"I have a FMS with GPS and IRS. The SID is based on a VOR/DME. Can I use it with the VOR u/S?"

probably not, legaly speaking, but with such FMS you have a navigation accuracy way better than with the VOR/DME, so you can accurately fly the damned SID.

In the case of a non GPS FMS, probably you can fly it very accurately too, as long as you have estimated position error of 5 or less, which is what a VOR/DME gives. after take off, IRS alone is better than 5.

27th Jul 2011, 13:16
Nice Information.Thanks.
Hosts101.com (http://www.hosts101.com/)

27th Jul 2011, 19:49
In my airline we can do it, as the approach is in the database, provided accuracy is HIGH. I will have a look for the reference. Im sure I read about it, but today a just cant find it:ugh:

To be continued....

27th Jul 2011, 20:03
From the FCOM (737NG)

Raw Data Monitoring

During localizer-based approaches (ILS G/S out, LOC) applicable raw data must be monitored throughout the approach.

During non-localizer based approaches where the FMC is used for course or path tracking (VOR, TACAN, NDB, RNAV, GPS, etc.), monitoring raw data is recommended, if available.

During single FMC, single IRU, or single DME or single GPS operation, in the event the single operational FMC, IRU, DME, or GPS fails during the FMC approach, there must be a non-FMC means of navigation available for a missed approach such as VOR/NDB raw data and/or radar, and there must be a non – FMC approach available. Failure of the remaining single DME need not be considered if GPS updating is being used.

Which means under normal operation (2 FMC 2 GPS) there is no need to monitor the navaid on which the approach is based (except for LOC/ILS/GLS). It is of course recommended, but not required.

27th Jul 2011, 21:05
Hi Kijangnim, Denti & Dutchone,

I agree it is permitted to perform RNAV approaches with no ground based radio aids necessary - but they are specific approaches, (called RNAV or GNSS etc).
I thought that if the NPA approach plate specifies a radio aid - then it must be working - else you have to do a different approach.

e.g see Page 37 of this document:
AirbusSafetyLib_-FLT_OPS-GEN-SEQ02.pdf (http://www.airbus.com/fileadmin/media_gallery/files/safety_library_items/AirbusSafetyLib_-FLT_OPS-GEN-SEQ02.pdf)
It shows the same profile as the VOR Canarsie Approach at JFK, except it is called RNAV. If the VOR Carnasie is US - then you can't do the VOR approach - but you may do the RNAV approach - because there is one published.

27th Jul 2011, 23:37
As you can see in the excerpt above, it mentions specifically NDB, TACAN and VOR approaches and that monitoring is recommended, but not required.

If an NDB DME approach for example requires a DME that is co-located with an ILS i cannot use that nav aid for technical reasons as i can not use any ILS frequency when flying an NDB approach, the approach mode would try to fly the ILS instead of the NDB approach. However it is still legal to fly the approach without monitoring that DME as long as i have two FMC and 2 GPS.

In theory the nav aid needed for the approach must be working, however if i'm not monitoring that nav aid it becomes a theoretical issue as i won't see if it becomes inop during the approach.

28th Jul 2011, 06:23
Hi Denti,

Do you not have this problem with yours then?


Last Ditch
28th Jul 2011, 12:54
This needs to be answered in two parts-
1. Approach- Its illegal. As such ATC will not clear you for such an approach where the applicable Navaid is U/S.
2. Departure- You can depart provided you meet the minimums criteria considering the Navaid U/S..... or an appropriate takeoff alternate has been filed etc.

Again, if the onboard system is on MEL, you cannot consider the applicable Navaid to be available... legally speaking.

28th Jul 2011, 16:05
I guess it is the Bulletin about FMC version 10.8 which was immediately revoked and replaced with 10.7 until a fixed version 10.8a became available, about three months ago for us. Still doesn't change that you do not have to monitor the nav aid as the FMC computed GP can be deselected independently of the still correct ground track.

28th Jul 2011, 16:15

28th Jul 2011, 17:27
I sincerely hope I'm not a passenger down the back if you proceed with an approach without the published radio aids working.

Those days are gone!!!!

We are being cleared to fly an entire RNAV GPS approach in the A330/A340, with NO ground based stations, no DME, NO VOR, NO ILS etc...

All altimeters must be absolutely verified correct QNH (as there is no ground fix for comparison) and for temperature (in case of extreme cold) and the APPROACH is armed and flown to minimum coupled, and so far it will work fine.
RAIM needs to be verified. (satellites available at the start of the approach).

If the approach at destination is RNAV only, then alternate needs to be ground based stations, in case the approach cannot be flown, you wouldn't want to divert somewhere where there are no satellites available (time or position of the satellites) either.

I believe the goal is to have all approaches RNAV by 2016 if I remember.

SBAS and GBAS (satellite or ground based augment system ) will allow an autoland without ILS station, as far as I understand it, but the aircraft needs to have this equipment to read this.

28th Jul 2011, 17:59
can we use an fms waypoint in leu of an inop approach or departure navaid? I do not see anything there about RNAV/GPS.

28th Jul 2011, 18:43
I guess of the original poster would elaborate on the conditions, procedure type, etc...it would help....

it would be difficult to suggest using a waypoint in the box that is not part of the original procedure...