T.10 GROUND PROXIMITY WARNING (00:20)
BACKGROUND INSTRUCTION
BACKGROUND GPWS
The Airbus family is equipped with GPWS. Most GPWS alerts and warnings are generated as a result of changes in radio altimeter height or rate of those changes. The system predicts potential hazard from these trends but has no forward-looking capability. GPWS alerts and warnings are described at the end of this section.
EGPWS
The Enhanced GPWS incorporates the functions of the basic GPWS with the following added features:
Terrain Clearance Floor (TCF), Terrain Look Ahead Alerting and Terrain Awareness Display (TAD).
The purpose of the Enhanced GPWS functions is to provide a better situational awareness to the crew through the TAD, and to give earlier Cautions and Warnings to the pilot to initiate a safe recovery manoeuvre.
The computer incorporates a world wide Terrain Data Base with varying degrees of resolution.
It has also an airport data base. The earth is divided into grid sets with the record of the highest terrain altitude in each element of the grid. The
resolution of the data base is a function of the geographic location. There are 5 levels of resolution from High Resolution around an airport, and Small Resolution away from an airport.
The EGPWS determines present position, track and ground speed, which is used to advise the crew of any potential conflict with terrain. When the terrain violates specific computed boundaries on the projected flight path of the A/C, the associated threats will be announced to the crew.
The Enhanced GPWS is commanded ON from on the overhead panel by the TERR pushbutton located next to the other GPWS pushbuttons.
The two EGPWS functions provide displays on the ND. As the ND can only display one type of information at one time there are two specific pushbuttons which control the intentional display of terrain information or radar information.
The basic GPWS functions remains unchanged. The EGPWS functions are based on a terrain database and the FMGC current position, not on radar return.
The EGPWS has priority over the PWS.
The three EGPWS functions
1. FORWARD-LOOKING FUNCTION
The forward-looking function computes two terrain envelopes from the aircraft position, speed and track and adds a safety margin. These two terrain
envelopes are projected on the terrain data base and are coupled with the
FMGC position. When a conflict is detected between these terrain envelopes and the terrain memorised in the data base, an alert is triggered.
If the CAUTION envelope is penetrated, the areas which violate the caution envelope appear in a solid yellow with associated warnings.
The Caution Alert is:
1) - TERRAIN AHEAD, repeated every 7 sec 2) - GPWS RED LIGHT
3) - TERRAIN AHEAD in amber appears on the ND,
4) - TERRAIN data displayed on ND with SOLID YELLOW areas This caution gives typically 60 sec reaction time prior to potential terrain conflict.
If the WARNING envelope is penetrated, the areas which violate the warning envelope appears in a solid red with associated warnings.
The Warning Alert:
1) - TERRAIN AHEAD, PULL UP repeated continuously 2) - GPWS RED LIGHT
3) - TERRAIN AHEAD in red appears on the ND,
4) - TERRAIN data displayed on ND with SOLID RED areas This warning gives typically 30 sec reaction time.
2. TERRAIN CLEARANCE FLOOR FUNCTION
The terrain clearance floor envelope is stored in the data base. It envelopes the earth at 700 ft AGL and commences reducing to ground level 15 nm around the runways stored in the data base. Consequently it is below a level that an aircraft would normally be during an approach. If the aircraft enters this envelope, an alert is triggered. The warning is a function of the FMGC aircraft position a nd radio altitude and complements the GPWS warnings.
The TCF is available in ALL FLIGHT PHASES and is a complement to the basic GPWS mode 4.
The TCF Alert:
1) - TOO LOW TERRAIN, TOO LOW TERRAIN 2) - GPWS RED LIGHT
3. TERRAIN AWARENESS DISPLAY FUNCTION
The TAD function displays an image of the surrounding terrain on ND (except in PLAN mode).
The display is generated by comparing the aircraft altitude to the terrain data base coupled with FMGC position.
The terrain is not shown if terrain altitude is more than 2000 ft below aircraft altitude or if its elevation is within 400 ft of the runway elevation nearest the aircraft. A colour code is used otherwise from black to red.
A different image texture, an image display which sweeps from centre outward to both ND side and a TERR indication instead of TILT indication help the crew to make the difference between the EGPWS terrain computed data and the ground picture sensed by the radar.
TAD function is to be used for Terrain Awareness, but not for navigation.
OPERATIONAL RECOMENDATIONS
The EGPWS can be used only if GPS PRIMARY or navigation accuracy check is positive. The EGPWS functions are automatically deselected when navigation accuracy is low. In that case TERR STBY then appears on the ECAM memo. If GPS is not primary, and the Navigation accuracy
check is negative then switch off the EGPWS with the TERR pushbutton on the overhead panel.
Airbus recommends that for an approach where terrain is suspected the PNF has TERR ON ND - ON and the PF has TERR ON ND – OFF.
If TERR ON ND pushbutton is pressed off and an EGPWS terrain caution or warning is triggered, the terrain data is automatically displayed on the ND, and the TERR ON ND light comes on.
The brightness of terrain indication on the ND is controlled via the weather radar control knob. Thus, when a terrain alert occurs, the ND weather / terrain display brightness may need to be adjusted.
TAD and TCF function use FMS1 position to perform their calculations.
Therefore, an FMS1 position error may induce erroneous information and warnings.
TAD function computes the aircrafts relative altitude by using the Captains barometric setting information. Therefore, if the barometric setting is incorrect the TAD function will also provide erroneous information and / or warnings.
In case of any warning including “PULL UP”, immediately and with no arguments:
- Set TOGA - Pull full aft stick
- Check speed brake retracted - Maintain initially wings levelled.
In case of any terrain, descent or configuration alerts - Adjust flight path or go-around or
- Climb and turn as necessary or - Adjust configuration or go-around
- Re-establish on G/S or press G/S mode pushbutton if undue alert Care must be taken when operating on one engine, with flaps extended and at light weight as in this configuration directional control may be difficult. The drill must be carried out positively, with clear announcement of intent, positive control action and the control input retained until clear of danger.
GPWS BASIC FUNCTIONS
The fi ve functions of the basic GPWS are:
MODE 1: Excessive Descent Rate
Warns that the aircraft descent rate with respect to altitude above ground level is excessive. Available in all flight phases.
The Mode 1 Alert:
1) - SINK RATE (twice)
2) - then PULL UP (continuously) 3) - GPWS RED LIGHT
MODE 2: Excessive closure to Terrain
Warns of rapidly rising terrain with respect to the aircraft.
The Mode 2 Alert:
1) - TERRAIN - TERRAIN
2) - then PULL UP (continuously) 3) - GPWS RED LIGHT
Mode 2A active during climb out, cruise, initial approach when Flaps are not in landing conf and the aircraft is not on the Glide Slope centre line.
Mode 2B is de-sensitised to permit landing manoeuvres close to terrain without undue alerts.
It is automatically engaged when the Flaps are in Landing Conf, or within 2 dots of the G/S. With LDG GEAR down and flaps landing conf, the PULL UP call is suppressed.
MODE 3: Altitude Loss After T/O
Warns of a significant altitude loss after take off or low altitude go around (>
245 ft) with gear or flaps not in landing conf.
The Mode 3 Alert:
1) - DON'T SINK
2) - GPWS AMBER LIGHT MODE 4: Unsafe Terrain Clearance
Warns of insufficient terrain clearance as a function of the phase of flight, speed and / or aircraft configuration.
The Mode 4 Alert:
1) - TOO LOW TERRAIN
2) - TOO LOW GEAR (500 ft R/A) TOO LOW FLAPS (245 ft R/A) 3) - GPWS AMBER LIGHT
This mode is divided into three sub -modes:
Mode 4A Cruise approach with Gear Up. This provides alerting for cruise for flight into terrain where the terrain is not rising significantly or the aircraft is not descending rapidly:
1) - TOO LOW TERRAIN
2) - TOO LOW GEAR (if R/A < 500, IAS < 190).
Mode 4B Cruise approach with Gear Down and Flaps not in landing Conf:
1) - TOO LOW TERRAIN
2) - TOO LOW FLAPS (if R/A < 245, IAS < 160)
Mode 4C After takeoff or low altitude Go Around when Gear or Flaps are not in landing conf.
It warns the crew that the terrain is rising more steeply than the aircraft is climbing. A Minimum Terrain Clearance (MTC) is defined and increases with R/A up to 500 ft if IAS =190 kts and up to 1000 ft if IAS increases to 250 kts:
1) - TOO LOW TERRAIN.
Mode 5: Excessive G/S deviation
Warns whenever the aircraft descends below the glide slope.
The Mode 5 Alert:
1) - GLIDE SLOPE, GLIDE SLOPE
2) - GPWS AMBER LIGHT
It starts below 1000 ft RA, and the loudness and rate of the message increases. Below 150 ft RA it is desensitised to reduce nuisance alerts.
Pressing the glideslope pushbutton stops the alert and turns off the amber G/S. In case of a further violation the alert returns.
The landing configuration is by DEFAULT FLAPS FULL. If landing is to be performed in FLAPS 3 the LDG FLAP 3 pushbutton should be selected ON on the OVHD panel. The Flap mode is then inhibited when CONFIG 3 is
selected.
In this case ECAM LDG MEMO displays FLAPS ……… 3 rather than FLAP
……… FULL.
Note that on MCDU PERF APP page, LDG CONF selection computes VLS and associated deceleration prediction but is not connected to GPWS.
INSTRUCTION
In order to demonstrate the EGPWS functions you must explain to the
trainees that for the purposes of demonstration they have to ignore the GPWS warnings and the EGPWS Caution in order to see the EGPWS Warning. After take off get them to maintain level flight at approximately the height of some terrain feature. As the aircraft flies towards the terrain the first warning is the GPWS Mode 4 saying TOO LOW TERRAIN and normally this is enough for a pilot to commence recovery. However you must explain that for purposes of demonstration they will maintain their current path and the next event will be the EGPWS Caution with the TAD pop up. Still for purposes of demonstration they maintain their current path and then they will get the EGPWS Warning Alert at which time they should carry out the Emergency recovery procedure.
T.011 VAPP DETERMINATION (00 :10)
VAPP NORMAL CONFIGURATION VAPP ABNORMAL CONFIGURATION GS MINI PROTECTION
VAPP NORMAL CONFIGURATION
VAPP is computed as a factor of VLS (1,23 VS1G) of the landing configuration.
In 95% of the cases the FMGC provides the correct VAPP on the PERF APPR page, once FLAP 3 or FLAP FULL landing configuration has been inserted, as well as the tower wind.
Be aware that the wind direction provided by the Tower or ATIS is given in the same reference as the runway direction (magnetic or true) whereas the wind provided by VOLMET, METAR or TAF is always true.
On PERF APPR, the FMS considers the wind direction to be in the same reference as the runway direction; therefore if the airport is magnetic referenced, insert the magnetic wind direction.
VAPP is computed at the predicted Landing Weight while the A/C is in CRZ and DES phases.
Once in APPR phase, VAPP is computed using the current Gross Weight.
It is possible to insert a lower VAPP (minimum of VLS) if there is no wind, provided the landing is performed manually with ATHR OFF and there is no ice or expected downburst.
It is possible to increase the VAPP in case of a strong suspected downburst.
In that case, VAPP = VLS + max 15 kts can be inserted.
VAPP ABNORMAL CONFIGURATION (slats / flaps, flight controls etc).
When a slats / flaps abnormal configuration occurs, the PFD displays a correct VLS related to the actual slats / flaps configuration, unless both SFCCs have failed.
In some of these abnormal configurations, it is advisable to fly at a minimum speed higher than VLS to improve the handling characteristics of the A/C. The ECAM then gives the value to be added to the VLS value displayed on the PFD.
In order to prepare the approach a nd landing, the pilot needs to know VAPP in advance, but the VLS is not necessarily available at that time on the PFD because the A/C flies at a higher speed or because the abnormal CONF is not yet reached. In this case VAPP will be determined using the QRH. The
principle is to refer to VREF (VLS CONF full), which can be read on PERF APPR or QRH, and to add VREF from the QRH table.
GS MINI PROTECTION
In order to benefit from Ground Speed mini protection you have to fly with managed airspeed.
The purpose of the GS mini protection is to always keep the A/C energy level above a minimum value, regardless of the wind variations or gusts. This minimum level is the energy the aircraft will have at landing with the expected tower wind. The ground speed of the aircraft at that time which is called GS mini.
GS mini = VAPP – Tower head wind component
In order to achieve that goal, the aircraft GS should never drop below GS mini in the approach while the winds are changing. So the aircraft IAS will vary while flying the approach to cope with the gusts or wind changes.
The FMGS continuously computes an IAS target speed, which ensures that the aircraft GS is at least equal to GS mini. The FMGS uses the
instantaneous wind component experienced by the aircraft.
IAS Target Speed = GS mini + Current headwind component
This target speed is limited by VFE-5 in case of very strong gusts and, by VAPP in case of tailwind. If instantaneous wind is lower than the tower wind;
below 400ft, the effect of the current wind variations is smoothly decreased so as to avoid too high speeds in the flare (1/3 of current wind variations taken into account).
To demonstrate the GS mini function insert a strong headwind so that as the trainees turn onto final they can see the managed VAPP increase due to the headwind.