G.05 FLIGHT IN SEVERE TURBULENCE (00:05)
CONSIDERATIONS
CONSIDERATIONS
Flight in Severe Turbulence is not Type Specific so is not addressed in our Transition course. There are however some considerations that need to be discussed with your trainees.
The best advice is to avoid areas of severe turbulence either by use of the weather radar (for thunderstorms etc), at the pre-flight planning stage (clear air turbulence forecast in met briefing) or by a change of flight level if
turbulence is reported by preceding aircraft.
Cruise levels at close to maximum level should not be used when turbulence is anticipated, as there will be a much smaller margin between VMAX and VLS leading to the increased risk of over speed warnings or activation of low speed protections.
The appropriate speeds are to be found in the FCOM and QRH. Ensure the Cabin Crew are advised in time to finish and secure the cabin.
Both pilots (at all times) should have the lap and crotch part of their seat belts fastened. If the shoulder harnesses are unfastened and retracted there is no need to fasten them in turbulence. However, if the shoulder harness is locked before being removed from the central buckle in order to make it easier to refasten then it should be fastened as the metal buckle will hurt if it hits you due to the turbulence.
Keep in mind that the simulator is designed with certain limits and these affect its ability to faithfully represent movement in the rolling and yawing planes.
G.06 GLOBAL POSITIONING SYSTEM (00:15)
BACKGROUND INSTRUCTION
BACKGROUND
The GPS is a satellite based radio navigation aid. GPS PRIMARY is an Airbus term defining an operational concept. It means that adequate GPS accuracy and integrity are provided and that GPS is available as the basis for the FM position. The GPS fitted to the Airbus family of aircraft monitors the integrity of the position information provided, and gives indications of when this position information cannot be relied upon.
FMGS position calculation.
The position calculated by the twin GPS receivers is added to the IRS calculated position producing a GPIRS position. This is then fed to the FMGC’s and a FM position is produced. At take off, even with GPS, the FM position is updated to runway threshold (+ T/O SHIFT if applicable). The FMGC’s will use the GPIRS position as the FM position so long as GPS PRIMARY is indicated on the MCDU PROG page.
Reasonableness tests on the GPIRS and IRS positions are carried out and any unreasonable position is disregarded for the purpose of FM position calculation. The table below summarizes how FM position is derived with and without GPS PRIMARY
FM POSITION WITHOUT GPS WITH GPS
On ground before take-off Mix IRS position GPIRS At take-off Runway threshold (+ T/O shift) GPIRS
Flight MIX IRS & Radio Position
-(tending towards Radio Position)
GPIRS
Flight without GPS or Radio Position update
MIX IRS position + Last memorised FM position, gradually tending towards IRS position
Not
applicable
FCOM section 1.22.20 FCOM 4.02.20 provides a full description of FMGS position computation.
During flight preparation, GPS PRIMARY will be indicated on the MCDU PROG page and the ND.
This message should be cleared using the CLR pushbutton. This is a positive confirmation to the crew that GPS is accurate.
The GPS workings are transparent to the crew and will only require attention in the case of a fault or a downgrading of the position information. If the GPS status changes, a message will be displayed on the MCDU and ND.
The amber GPS PRIMARY LOST cannot be cleared from the ND and is to remind the pilots that GPS is not available. Navigation accuracy up-or downgrade will be shown in the same way as already used for non GPS navigation.
The following is a list of MCDU pages associated with the use of GPS and a brief description of their use:
MCDU PAGE FUNCTION
SELECTED NAVAIDS Allows de-selection or selection of GPS
GPS MONITOR Display of GPS positions and other GPS derived information
IRS 1 (2) (3) GPIRS Position for each IRS
PROG When GPS PRIMARY is shown, indicates that GPIRS is used for FM PROG position calculation.
Navigation accuracy is shown.
PREDICTIVE GPS* Displays information about the predicted availability of GPS at destination ETA or at a particular waypoint ARRIVAL Allows selection of GPS approach
Full descriptions of the above pages can be found in FCOM 4.03.20 The full GPS standard will permit predictions to be made regarding the
feasibility of a GPS approach at destination. The calculation involved relies on the number of, and the position of, the satellites at ETA. The “time window” is pilot modifiable.
The current status of GPS permits approaches to Cat 1 limits at best.
Individual certification authorities are discussing GPS accuracy, reliability and such. Thus, the minima and acceptance of GPS in each country must be checked before using GPS as a prime means of navigation in the approach phase.
There are two types of GPS approach:
A. GPS OVERLAY APPROACH
The aircraft performs an approach along the trajectory of a published non precision approach using GPS position information in GPS PRIMARY
navigation mode. Before beginning the approach a check of GPS PRIMARY and HIGH accuracy must be made which replaces the navigation accuracy check. Before the FAF check GPS PRIMARY and HIGH accuracy with a RNP of 0.3 NM or less. Raw data must be displayed and monitored at all times.
FCOM 4.05.70 details the procedures to be used. If raw data indicates that the aircraft is not on the required flight path the pilot must revert to raw data to correct the flight path.
B. GPS STAND ALONE APPROACH
The aircraft is guided along the trajectory of an approach the waypoints of which are not referenced to any ground base navigation aid.
If GPS PRIMARY is lost during a GPS Stand Alone Approach, a GPS
PRIMARY LOST message in amber will be displayed accompanied by a triple click. If this occurs or there is a navigation accuracy downgrade a Missed
Approach is normally carried out, unless raw data allows for a satisfactory continuation.
INSTRUCTION
Our syllabus is mostly based on GPS being Primary. There can be a situation where there is a NOTAM stating that during a certain period satellite
navigation is unavailable. In this case GPS Navigation shall be deselected from the Radio Navigation FMGS page.
If GPS Navigation has been de-selected and the crew is flying a Managed Approach after checking the Navigation Accuracy you can force them into a Selected Approach by inserting a Slow Map Shift.