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-   -   Are Engine- out SIDS supposed to be flown in Selected guidance (https://www.pprune.org/tech-log/619580-engine-out-sids-supposed-flown-selected-guidance.html)

C.M 18th Mar 2019 20:25

Are Engine- out SIDS supposed to be flown in Selected guidance
 
I’ve heard on accasions that Manually created engine-out SIDs , if actually used in engine-out conditions , should not be flown in managed guidance (NAV mode in airbus terminology / LNAV mode in Boeing terminology ) but should be flown in Selected guidance ( I,e heading mode ) . Is anyone aware of this and where this piece of information can be found ? ( I was told it could be found in the Airbus FCOM ( couldn’t find it ) and was later told that was mentioned in ICAO documentation ...

FE Hoppy 18th Mar 2019 20:29

The reason is bank angle. Engine out at V2- v2+10 you don't want to be using 30° bank as you don't have the margin. Hence "Heading Half bank" on many types.

Check Airman 18th Mar 2019 20:45

Without referencing the manuals, off the top of my head, doesn't the 320 already provide bank angle protection if single engine?

EGPFlyer 18th Mar 2019 22:21

Yes, 15 degrees up to maneuvering speed -10 and then linearly increasing to 30 degrees at maneuvering speed -3 in NAV. If your in track or heading the max is 25 degrees

IBE8720 19th Mar 2019 08:43


Originally Posted by C.M (Post 10422855)
I’ve heard on accasions that Manually created engine-out SIDs , if actually used in engine-out conditions , should not be flown in managed guidance (NAV mode in airbus terminology / LNAV mode in Boeing terminology ) but should be flown in Selected guidance ( I,e heading mode ) . Is anyone aware of this and where this piece of information can be found ? ( I was told it could be found in the Airbus FCOM ( couldn’t find it ) and was later told that was mentioned in ICAO documentation ...

I was told the same thing when I first started on the A320. Yet could never and was never shown where it was specifically written.
I have chased the answer for 6 years. All I can find is in Limitations, Auto Flight, it tells you when you can and can’t use NAV. I think there has been a change in this Limitation and can’t find a Limitation on NAV mode related to pilot created waypoints (specifically related to EO SID).

If someone can provide a reference in FCOM, please do.

OPEN DES 19th Mar 2019 10:01


Originally Posted by EGPFlyer (Post 10422988)
Yes, 15 degrees up to maneuvering speed -10 and then linearly increasing to 30 degrees at maneuvering speed -3 in NAV. If your in track or heading the max is 25 degrees

The autoflight bank limitations apply to all FD roll-modes in Airbus FBW not only NAV.
With FD off there is no decreased bank-limit for OEI; it is an autoflight limitation only.

With regards to manual eosid construction and use of NAV mode:
-Remember that the EOSID is a non-published operator contingency procedure, hence there is no RNP specified for this type of procedure.
-There are no limitations however be cautious with manually constructed segments (PBD’s etc), the validation of the tracks and distances in the briefing stage is very important here as there has been no prior database validation. Be ready to take-over in selected modes, having raw-data back-up with radnav tuning is a good idea.
-don’t rush down heads down to activate the secondary fpl, much better to fly a close turn in selected modes to then eventually rely on the secondary once safely away from the ground.

Skyjob 19th Mar 2019 10:40

EOSIDs are created with a set of parameters which include minimum and maximum bank angels.
Though they can be coded in database, no NAV or LNAV is able to use the bank angles required as they are variable depending on configuration and manoeuvre capability.
Reason why these are NOT to be flown in managed guidance is to ensure the parameters are not exceeded for phase of flight.
If a procedure bank angle requires 20 or less for obstacle clearance turn radius, while NAV can manage 25 due configuration, it will fly 25, possibly then encroaching an area avoided by calculations of obstacle clearance.
For straight out segments and turns after initial limitations are overcome, managed guidance works a treat!
Managed guidance is not always a better option, but does aid the pilots in a visual representation at all times.

IBE8720 19th Mar 2019 12:25

Where is the reference?
I was told it is an Airbus limitation, therefore it MUST be written in the Airbus Manuals somewhere. Everyone seems to know you don’t fly in NAV, but no one seems to be able to indicate where it is written.

Skyjob 19th Mar 2019 14:04

"On airbus fly-by-wire aircraft, the autopilot limits the bank angle at takeoff with one engine inoperative to 15°. Some Engine Out Standard Instrument Departures (EOSID) require a turn to be performed with a bank angle of 20° or more. When a turn with more than a 15° bank angle must be carried out, the aircraft must be manually flown." Airbus - Flight Operations Support & Line Assistance - getting to grips with aircraft performance

The loss of gradient versus the bank angle is provided in the Airbus Flight Manual (AFM), as well as in the Airbus Performance Program Manual (PPM).

In addition from FAR:
  1. Bank Angle. FAR Sections 121.189, 135.379 and 135.398 assume that the airplane is not banked before reaching a height of 50 feet, and that thereafter, the maximum bank is not more than 15 degrees. Obstacle clearance at certain airports can be enhanced by the use of bank angles greater than 15°. The following bank angles and heights may be used with Operation Specification authorization (in accordance with FAR 121.173 (f)). Any bank angles greater than the values shown below require additional specific FAA authorization:
    1. Height (above Departure End of Runway - ft) v Maximum Bank Angle (degrees)
      • h>400 25 degrees
      • 400>h>100 20 degrees
      • 100>h>50 15 degrees

reptile 19th Mar 2019 15:27

https://cimg0.ibsrv.net/gimg/pprune....b0eb5f4da2.jpg
FCTM -> PR ->AEP -> ENG -> Engine Failure After V1 (A319/A320/A321)

The bank limit is addressed in the diagram.

Smythe 19th Mar 2019 16:22

Some very good detail here: AirbusFlight Control Laws

MECHANICAL BACKUP
In case of a complete loss of electrical flight control signals, the aircraft can be temporarily controlled by mechanical mode.
  • Pitch control is achieved through the horizontal stabilizer by using the manual trim wheel.
  • Lateral control is accomplished using the rudder pedals.
  • Both controls require hydraulic power.
  • A red MAN PITCH TRIM ONLY warning appears on the PFD.

Check Airman 19th Mar 2019 23:24


Originally Posted by EGPFlyer (Post 10422988)
Yes, 15 degrees up to maneuvering speed -10 and then linearly increasing to 30 degrees at maneuvering speed -3 in NAV. If your in track or heading the max is 25 degrees

My manuals don't specify NAV mode only. The FD limits the bank angle in an engine out scenario in all lateral modes. Here's what my book says about engine out guidance. Sorry for the formatting.


• The system limits autopilot (AP) and flight director (FD) bank angles during takeoff and approach phases as follows:
• 15° when the aircraft speed is below the maneuvering speed (F, S, or Green Dot speed) – 10 kt
• Then linear increase to 25° up to maneuvering speeds (F, S, or Green Dot speed) – 3 kt
• 25° above maneuvering speeds (F,S, or Green Dot speed) – 3 kt. Note: The engine-out bank angle limits apply, when the FG part of the FMGS has detected an engine-out. It cannot be cleared by the crew through the MCDU E.O CLEAR prompt.

To the OP, I've never heard any mention of any restriction on the kind of guidance used for an engine out procedure. At several airports (particularly hot and high locations) you'd absolutely want managed guidance.

HGVO 20th Mar 2019 08:32

In our company we are not allowed to use NAV Mode below MSA until all turns of the EOSID are completed. Further we are not allowed to use NAV mode to pilot created waypoints at any altitude...

aterpster 20th Mar 2019 13:32


Originally Posted by Skyjob (Post 10423563)

In addition from FAR:
  1. Bank Angle. FAR Sections 121.189, 135.379 and 135.398 assume that the airplane is not banked before reaching a height of 50 feet, and that thereafter, the maximum bank is not more than 15 degrees. Obstacle clearance at certain airports can be enhanced by the use of bank angles greater than 15°. The following bank angles and heights may be used with Operation Specification authorization (in accordance with FAR 121.173 (f)). Any bank angles greater than the values shown below require additional specific FAA authorization:
    1. Height (above Departure End of Runway - ft) v Maximum Bank Angle (degrees)
      • h>400 25 degrees
      • 400>h>100 20 degrees
      • 100>h>50 15 degrees

Lots of performance loss at 25 degrees. No doubt any FAA authorization would come only after a comprehensive planning and performance analysis.


Check Airman 20th Mar 2019 13:41


Originally Posted by HGVO (Post 10424376)
In our company we are not allowed to use NAV Mode below MSA until all turns of the EOSID are completed. Further we are not allowed to use NAV mode to pilot created waypoints at any altitude...

Odd some of the restrictions that different companies come up with.

Skyjob 20th Mar 2019 17:01


Originally Posted by Check Airman (Post 10424662)
Odd some of the restrictions that different companies come up with.

Think to poster's airline makes a valid point in its restriction, as it means NAV is not allowed below the obstacle critical altitude being MSA.
Once above MSA, obstacles are no longer assessed, thus NAV is safe to be used.
It ensures crew restrict themselves from overbanking and obstacle proximity by using Selected Guidance with its imposed bank angle limits.

sonicbum 20th Mar 2019 18:48


Originally Posted by Skyjob (Post 10424838)
Think to poster's airline makes a valid point in its restriction, as it means NAV is not allowed below the obstacle critical altitude being MSA.
Once above MSA, obstacles are no longer assessed, thus NAV is safe to be used.
It ensures crew restrict themselves from overbanking and obstacle proximity by using Selected Guidance with its imposed bank angle limits.

I believe the restriction on using NAV below MSA for pilot's created waypoints is primarily due to CFIT prevention. The "overbanking" is not really an issue in Airbus FBW in both Hdg/Trk and NAV mode.

FlightDetent 20th Mar 2019 20:35

We used to fly overlay, manually created LNAV guidance for VOR approaches to airports not in FMS database on the 737 with 2 IRS and no GPS. Not the slightest problem.

Now, Airbus themselves (were made to) claim flying VOR NPA from the box with the underlying NAVAID being U/S is OK, as long as some very relevant precautions are taken.
And at the same time, Airbus prohibits use of NAV for manually created approaches. Que?

The explanation, the very same I believe applies to OP's question, is that the restrictions are operational - i.e. avoiding human error and the training cost - and not technical. Agreed with Check Airman and sonicbum. The idea you can create a waypoint but not allowed to fly them in NAV is completely silly (respecting peculiar applications in the terminal and approach area).

C.M 22nd Mar 2019 20:53

Sum up
 
The engine-out SIDs that most companies fly are defined by a competent source supposently after a study of the surrounding terrain . Also it is the duty of the performance engineer of each company to check all these parameters and I guess a check of any consideration of angle of bank be taken into account . So yes we are talking about manually created engine out SIDs but that we have been given to construct. To make a global ban of managed guidance for the engine out SIDs seems stupid to say the least .
1.We throw the concept of “max use of automation in emergency” out of the window ,
2. There is no quarantee that a critical turn will always be noticed while being concentrated on ECAM , if flying on selected guidance . The likelihood of messing up a EOSID and the associated risk , far outweighs any likelihood of dealing with any performance loss due to increased Angle of bank.
3. Were an increased / decreased angle of bank becomes important , then and only then should considereration be given to this fact and such consideration be stated in the EOSID to decide on the level of automation .

C.M 23rd Mar 2019 07:18

IBE8720 , the limitation in the autoflight chapter you are referring to , is the use of NAV when flying Non precision approaches with single engine . Also this limitation applies to the Thales FMGC and not for the Honeywell FMGC . So this limitation is completely unrelated to the use of NAV for EOSID .


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