Originally Posted by
gulliBell
In the APP1 mode that they were in, when they were at 200' ASL on final approach and stable, pitch is maintaining altitude, and power is maintaining airspeed. Correct? So the autopilot was driving the pitch axis to maintain height, correct? What was driving the power, was this being controlled manually by the pilot, or automatically by the AFCS? AFCS, a rad alt coupled mode and A/S If the power was being manipulated manually, and the speed got too slow, I assume at some point the AFCS will pitch up abruptly (when it gets on the back side of the power curve) trying to maintain the selected height? I'm not familiar with S92, but this behaviour has all the attributes of S76. A pitch mode being used to maintain height, but not enough power being applied to maintain speed after levelling off. Especially after a low power descent, levelling off, but not applying power. The airspeed will very slowly bleed off, which might not be noticed by the crew, until it gets to a point where AFCS commands abrupt pitch up, airspeed rapidly decreases, and then things are out of control.
Am I right in saying that the aircraft was out of control before it hit the rocks, because insufficient power was applied for the flight mode they were in? And if they didn't hit the rocks the result would have been the same? We demonstrate this in the simulator, once that rapid pitch up occurs, without immediate corrective action, the aircraft will just fall out of the sky and you need more than 200' to recover the situation. I've seen experienced crews make this mistake; it happens in 2 different manoeuvres. Single engine missed approach using vertical speed mode to climb, but not applying enough power, and low power descent using ALT PRE, capturing the new height but not applying power.
Based on the report, I believe the pitch up was in response to seeing the island at the last moment. Been there, seen that...
The short time period from the the crewman calling an obstacle to impact (9 seconds) was insufficient for her to adjust her SA from believing that the small island that had, in her view of the local area, moved from behind to in front of the aircraft and was much higher than expected. This is not a condemnation of her, rather my view that once they were at that point, it takes time for that profound a recalibration of SA. Even the crewman's initial statement seems to be not yet fully aware of the danger for a few seconds....
HeliComparator:
As I tried to say earlier, in my view it points to the flawed culture in SAR of always trying to get low / VFR as soon as possible. In my experience SAR pilots are far happier flying around at 200' VFR below cloud in the crud, rather than being at MSA IFR in cloud. Of course getting "down and dirty" asap can sometimes be the right thing to do, but not always. It surely can't be right to need to descend to 200' so far from the destination during an instrument letdown.
In this case, looking at the route guide, I would say it is not an instrument letdown. This is not an approach. It is a visual route to be flown to avoid terrain while approaching an off airport destination. As such, reaching and maintaining VMC while still offshore is probably required.
Al-Bert
Unless things have changed in the last 18 years since I was there in a Seaking there are no plates or IFR procedures to remote sites such as Blacksod. We would, if IMC, have carried out a radar letdown overwater on our search radar, possibly but unusually to full FCS hover, and then radar guided hover taxy if still v low viz but in sight of the surface, to the LS. I assume S92 operators have similar company procedures?
This leads to my comments below.
puntosaurus:
Sasless. Well I agree that there were lots of other mechanisms already in the cockpit that could have alerted the crew to the presence of the island, and one more (Txpndr) might have helped. But the fundamental problem appears to be that the crew clearly didn't know that BLKMO was above a large island, rather than a small rock (Carrick something or other) barely exposed at low tide.
If your IP is just a Lat/Long in the FMC, why on earth place it over the highest point around. The purpose of a letdown over water is surely to keep you away from the hard stuff until you are ready for it.
cnpc. Whoever drew up the approach knew the island was 282ft high, because he or she wrote it on the plate.
oden. The guys in the back knew they were headed for the island because they were looking at an image of it on a display. Presumably the crew were not looking at that display.
Again, just my opinion with limited information, but based on experience.
I would first investigate whether this 'route/procedure' predates the 92 and was faithfully copied on, with easily identifiable points from days before FMC guided 4-axis autopilots. Then the choosing of an easily identified visual waypoint clear of higher terrain makes sense to aid visual guidance into the bay.
As has been said, I think some systemic errors and traps will be found that set this crew up to be caught by a combination of poor weather and unfamiliar operating location. The difference between success and failure will be a hair's breadth...
Something we all work hard at trying to see in advance every day.
This was an absolute tragedy