f you flew A. GPWS and B. EGPWS equipped aircaft deliberately or otherwise toward steep rising ground as was the likely course of the Metro, in the landing configuration would you expect to get a PULL UP warning or any of the other modes.
Would you get a different warning if the gear and flaps were up?
Rough and ready answers?
A. Probably not. If the hill was much higher than you, and of a steep gradient, you might get insufficient warning or nil.
B. In most cases, yes.
Clean config or landing config make a difference? No. What you are talking about here is rate of closure, a Mode 2 warning. You would get a terrain closure warning ("WHOOP WHOOP Pull Up") well before you got to the 245'-1000' radio altitude that would trigger the unsafe terrain clearance mode 4 warnings.
On the topic of equipment failures and interference....
One of the things that you learn (or have beaten into you!) as you proceed through life as an IFR pilot, is that the information you need is duplicated many time over. You never rely simply on one source of information, or on one gadget to get you through a situation.
This is the state of mind and professional approach that IFR operators try to develop in their pilots.
For example, fuel calculations. Never just look at your gauges and say, great, I have 4 tonnes left in the tanks. You recall that you started with 9 tonnes. You then scan the fuel used totalizers and add them up. 5 tonnes burnt. 4+5=9. You start to feel reassured. You then think, departure was 2h15m ago, at just under 2 tonnes/hr, plus around 500kg for takeoff and climb to cruise.
One observation and two calculations to back it up as a check of its reasonableness. Why? Because fuel quantity gauges are gadgets, and gadgets sometimes malfunction.
How about an approach like an ILS?
Well first, you need to have those needles centred as you fly down. But it is best to start by flying over the locator beacon at a fixed altitude, normally 3000' fly level and intercept the glideslope from underneath. That way you have flown station passage straight over a known point at a known altitude and minimize the probability to capturing a false localiser course or a false glideslope. Gadgets. The glideslope will start down at a certain DME or GPS distance from the aerodrome. Crosscheck. In my Cat C aeroplane that flies down the ILS at around 125kts, I know that I will stay on slope if I have a rate of descent that is roughly 5x my groundspeed, about 650 to 700 feet per minute. I will know that I have set the correct QNH when I cross the outer marker at the outer marker check height. I know I have the right outer marker because I know it is located at 4.7DME. The GPS in the corner of my eye also says 4.7nm to run. When I hear the GPWS call out "Five Hundred" at 1.6DME that is good because that is the DME distance I should have a radalt of 500 and be on glideslope. I will know that I have the gear down and the landing flap set not only because the three green lights are glowing and the flap indicator show landing flap set, but also the aircraft is in a 2.5 degree nose down pitch attitude holding the reference speed plus 5 at a power setting of roughly 63% N1. All in the ballpark for a landing at 31 tonnes LW.
Lots and lots of information and knowledge, each little piece checked against another to confirm that I am where I am supposed to be. Any discrepancy is a niggly loose end, to sound a warning - 'what is wrong with this picture?'
And then there is a more experienced guy sitting to my left with the same questions running through his head, observing the same little bits of information and looking for the odd man out.
The point of all this?
1. Gadgets fail. The best of them do. Pilots love their gadgets. They use their gadgets. But a wise pilot never TRUSTS a gadget! Cross check everything one gadget says with another gadget, or the evidence of your eyes, or your quick calculations on your whiz wheel or calculator.
2. Passengers want safe pilots that look at everything when they board an aeroplane. Pilots need a working environment that supports them in gaining these skills, supports them in approaching their work with a critical and disciplined method. They dont want pilots that are struggling to get decent sleep, living near the poverty line, encouraged overtly or otherwise to be yes men, toeing a company line to get the job done. These skills are what brings out all the potential of the gadgets. It takes time, a lot of time, to get it together with all of the skills you need. Unfortunately as soon as these skills are gained they are lost to GA, because who wants to work so hard in such a terrible employment situation?