Q1: Summarise the purposes, operations and alerts of the various modes for GPWS.Ground Proximity Warning System, or for short GPWS, is a mean of warning the flight crew that they are flying into a terrain. It has a narrow operating range of 50 – 2,500 feet above ground level. As aircraft is coming closer to a terrain, the flight crew will be informed by a visual and aural alert. There is a total of 7 modes and I will each and every one of them.
Mode 1 – Excessive Descent Rate: “SINK RATE”, “PULL UP”Should an excessive rate of descent develop for the aircraft current altitude above ground level, the red panel on the red GPWS will flash and at the same time, the alert “SINK RATE” will be heard. If happen that the aircraft rate of descent still continues or worsens, it will then project “PULL UP”Mode 2 – Excessive Terrain Closure Rate: “TERRAIN, TERRAIN”, “PULL UP”Warns crew if aircraft is approaching terrain ahead. At first, it will say “Terrain Terrain”.
If pilot does not react to it, it will turn into a warning “Pull up, pull up”Mode 3 – Altitude Loss After Take-off: “DON’T SINK, DON’T SINK”Mode 3 informs the pilot of sudden descent and loss of altitude after take-off or during a missed approach. Should the aircraft descend while the aircraft is taking off, the red GPWS system will flash and at the same time, the alert “DON’T SINK, DON’T SINK” will be heard. Once the aircraft is cleared 1,000 ft above ground, mode 3 will disable.
Mode 3 will activate back when it detects a take-off or missed approach situation. Mode 4 – Unsafe Terrain Clearance: No gear, No flapsWhen the aircraft landing gear is yet to put down and locked at 500 feet above ground, the GPWS system will flash and at the same time, the alert “TOO LOW…, GEAR”. If flaps are not set for landing by 170 to 250 ft, the red GPWS system will flash and at the same time, the alert “TOO LOW…, FLAPS”Mode 5 – Excessive Deviation Below Glideslope: “GLIDESLOPE”An amber GPWS system will flash and at the same time, the alert “GLIDESLOPE” can be heard when the aircraft fails and fly below the glideslope. In the beginning, it will give out a much more “softer” and less repetition but it will become louder and repetitive as the aircraft deviation below glideslope worsens. Mode 6 – Excessive bank angle (Advisory Callouts): “BANK ANGLE”, “MINIMUMS”This mode is designed to give a situational awareness for the flight crew. As the pilot sets the radar altitude manually and the alert “MINIMUMS” at the selected altitude on the approach landing. When the pilot does over-banking to the aircraft, the alert “BANK ANGLE” can be heard and occur at present maximum.
Mode 7 – WindshearThe alert is only given out when the aircraft enters an area where headwinds rapidly decrease, tailwind increaseQ2. What are the enhancements EGPWS have over GPWS and summarise how they are accomplished?Enhanced GPWS or for short, EGPWS, provide present position, track and ground speed. Having this information could help the aircraft graphical planned view of the aircraft relative to the terrain and inform the flight crew about the terrain or obstacle they are heading towards to. Having an envelope modulation feature helps to reduce nuisance alerts by tailoring EGPWS alerts at certain geographic locations. On top of alerting the flight crew using visual and aural warning, it also uses a colour enhanced visual display of the terrain or obstacle relative to the forward look of the aircraft. The terrain display is provided on the weather radar called EFIS display or on the EGPWS display.
If EGPWS display is installed on the aircraft’s cockpit, the terrain information is reflected in the Terrain Awareness and Warning System, or for short TAWS display. It comes in 3 distinct colours. 16% green colour indicate terrain 1,000 to 2,000 ft below the aircraft current altitude.
50% green colour indicate terrain at a safe altitude below the aircraft down to 1,000 below. 25% yellow colour indicate terrain from 500 ft below the aircraft altitude and up to 1,000 ft above the aircraft. 50% yellow colour indicate terrain 1,000 to 2,000 ft above the aircraft. Lastly, the 50% red colour indicate terrain 2,000 ft or more above the aircraft current altitude.
On top of all that, it has terrain clearance floor, alerting the flight crew when it descends below a terrain clearance altitude where there are no runways.