757/767 weather radar/EGPWS Display

[757jetjockey]

Hi guys, does anyone know what the lower numbers are on the HSI when you have the EGPWS Terrain displayed???

thanks

JJ

[qwertyuiop]

Its the hieght of the lowest terrain showning in green.

[757jetjockey]

Ok, thanks for that...

however for clarity could you go into a bit more detail, i am aware that the EGPWS colours change in the same fashion as the weatrher radar returns do, but what is the scale that it uses??? abd when you say the lowest height displayed in green, would that not be the cut off point between displaying geen and yellow returns???

sorry if im talking rubbish...

JJ

[Charles Darwin]

If I am over water there may be a upper number of 100 and a lower number of 004. IF there is a 400´hill, there is for certain another of 300´ and a lower bank of 100´ etc. We often see values higher than the beaches that we are flying past.
The lowest terrain...strange... I think this number is more for us to evaluate the type of terrain ahead. If I see a 150/70 I know there are some highrise mountains ahead but if I see 100/90, there may be more of a plateau coming up.
I can´t see why we need to know the lowest terrain except for the above speculation.

[Shore Guy]

Most recent aircraft installations use the FMC derived position for EGPWS position.
If your FMC’s have map shift issues (read: non GPS updated position), the EGPWS will predicate its warnings (or more importantly, lack of) on this false “map shifted” position.
It has happened…..an Airbus nearly hit a hill in Africa due to map shift caused by rain damaged VOR equipment. EGPWS position was derived from FMC’s.
Some airlines have resolved this by installing a dedicated GPS to feed position information to the EGPWS. Many/most/perhaps all FMS’s not designed with GPS as part of their core design cannot be “upgraded” to accept GPS inputs.
A suggestion for any airline considering this addition/modification…..a comparator to annunciate FMC/GPS position difference greater than 1.0 n.m.…..a warning to crews they may be in a “map shift” scenario.
Be careful out there…..

[PEI_3721]

For a description of EGPWS indications and modes see EGPWS pilots guide (http://www.honeywell.com/sites/portal?smap=aerospace&page=Egpws-Home3&theme=T5&catID=CB54AACBB-D557-208D-8CE0-EC44CECAAB3B&id=HCA8A3ED3-7E1C-D7B4-9CAF-1F20D98A28AE&sel=8); note the new website address and additional information.
You will have to establish which version of EGPWS the aircraft is fitted with - 757/767 probably MkVI or VIII, but I haven’t flown those aircraft.

Take note of information given in recent papers at the FSF’s European Safety Seminar, which indicated that pilots operating knowledge of modern technology was very poor. One research paper looked specifically at weather Radar, another at the increasing number of ‘real’ EGPWS warning. Some crews did not understand how radar tilt worked, others did not know how EGPWS works, its limitations, or more importantly its capabilities.
EGPWS colour coding should not be compared with weather radar, they use different concepts.

EGPWS is very, very much more reliable than the old GPWS and does not suffer ‘nuisance’ warnings. Some aircraft might have problems due to ‘map shift’ from navigation sensor input (DME/FMS), but this can be eliminated by choosing the EGPWS varient with a GPS receiver embedded in the EGPWS computer.
The EGPWS ‘saves’ paper also strongly recommends activation of the Obstacle mode. A near miss incident was described where an aircraft almost hit a high rise building. The obstacle mode software is already in every EGPWS box and the upgrade and database is free from Honeywell. The aircraft may require a small wiring change.