Fedex MD11 - Subic Bay
 

03 Jun 02
1600Z
DCA02WA039
At Subic Bay
Philippines
MD-11 of FEDEX
Reg: N588FE

Elevator damage during escape maneuvers after ground proximity warning (GPWS) alert. Approaching Subic Bay at 8000 feet in heavy rain at the time.

Outboard portion of the left elevator had almost entirely separated and a small area inboard of this location was
missing.

^^^^^^^^^^^^^^^^^^^^^^^^^

Anyone have more information on this incident?

DC-10's and MD-11's are designed to shed the outer panels of their elevators when exceeding load limits.

A GPWS warning at 8000feet!:eek: Whats the MSA round there?

Hand Solo,

Most Enhanced GPWS (latest version) use a "3-D"database to compute terrain.

Original GPWS (Mk I) usually uses a feed from the Wx radar and the return is mathematically calculated to be cumulo nimbus or cumulo granite etc..

Certain size droplets, usually in very heavy rain, can have the effect of fooling the GPWS (Mk I) into the cumulo granite choice.

The problem is typically that the EGPWS (new version) does not wholly replace the original GPWS. The original version was usually just "overwritten", i.e. not deleted, and therefore occasionally the original system thinks it has something to say!

I do NOT know the details of the MD-11 event. I'm sure the situational awareness of the crew was such that they reacted as required to a GPWS alert in the conditions noted.

I've had the same problem in very heavy rain at 11,000 over Dallas (twice).

Considering you can stand on a six pack in East Texas an "see" El Paso, it's a non event.

Don't know the topography this crew was over though.

Cheers,

I have never heard of any GPWS system trying to determine Cumulo Granite from the Wx radar...

Is this specific to the MD-11? Or was it an early EGPWS?

All the GPWS I have flown with (A340, B757/767) are RAlt / VSI based, and the EGPWS we now have are terrain database dependent...

NoD

Within 25NM of apt highest MSA is 6800' to NW

I,m not sure about the feed from Wx radar into the GPWS I have however had a false GPWS "pull up" whilst descending into Corfu through heavy rain at around 10,000 ft. At 3AM it certainly concentrates the mind!

"DC-10s MD-11's are designed to shed the outer panels of their
elevators when exceeding load limits."

Bad things may happen when a load limit is exceeded but is there
any information that supports the notion that the separations that
occur are designed?

First, there may be differences between the two types mentioned
because of materials: composites are used for the MD-11 elevators
but I don't think that they were ever used in the DC-10 elevators.
Not sure about the latter, though.

I don't know anything about this particular incident but in the past
there have been several cases in which large portions of MD-11
elevators have been lost to fracture, delamination, and disbonding
of composite materials. There was an earlier Fedex MD-11 incident
(to N582FE) at Manila very much like this one. In that incident on
30 June 1999 a flight from Narita to Manila experienced a GPWS alert
while descending through 9500 ft on the approach in heavy rain. The
captain performed a GPWS escape maneuver. The event resulted in a
structural failure in the left elevator outboard counterbalance area.
The outboard end of the elevator and counterweight were found hanging
vertically on the outboard hinge bolt. The elevator lower surface
cracked and the upper surface delaminated.

Damage to elevators as the result of intentional stalls was known
from Douglas test flights. The earliest operational losses of portions
of the MD-11 elevators go back to incidents of Alitalia, KAL, and CI in
1992. The latter, mentioned in connection with PIO in the JAL 706 thread,
resulted in this recommendation:

"Require Douglas Aircraft Company to advise MD-11 operators of
the potential for damage to the composite elevators if the airplane is
operated beyond the limits of the design buffet boundary."

I did not see anything in the reports to suggest that Douglas was able
to precisely state what damage might occur or under what circumstances
that damage might occur. For instance, the language used went like this:

"DAC engineers believe that an MD-11 needs to exceed its buffet
boundary by a margin of 20 percent or more in order to sustain
elevator damage. The extent of severe damage is believed by DAC to
be related to some combination of the degree of exceedence above the
20 percent margin and length of time exposed to buffet. DAC has been
unable to determine the exact relationship.
...
DAC engineers were unable to determine exactly where the elevator
damage occurred or whether the amount of time outside the buffet
boundary exacerbated the elevator damage."

With regard to elevator safety design, Douglas did not mention
anything about benign separation - only redundance.

It would be interesting to know what forces were involved in
the two Fedex GPWS escape maneuvers. (Well, I'm not a pilot -
that's what is interesting to me.)

Hate to disagree but ..............
GPWS Mk1 inputs Rad Alt, Vertical Speed, Baro Rate.
GPWS Mk2 inputs Rad Alt, Vertical Speed, Baro Rate. just refined software and a couple more sub modes.
EGPWS inputs Rad Alt, Vertical Speed, Baro Rate, and PPos from FMC, FMGEC or whatever is knocking about. this is compared to what I believe is a fairly rudimentary terrain Db sort of like FS2000! hey it does the job.
Wx Radar haas never been an input to GPWS. I've installed enough of the various stages to know.
What concerns me a little is where someone can get the idea that Radar is an input. Is someone teaching this ?

"Is someone teaching this?"

Yes, probably a pilot, who is under the impression that...."pilots know everything". See the thread "I am an army of one" for proof of this phenomenon.

The terrain around Subic rises quite steeply to the east and southeast and pilots NEED to have situational awareness there...apparently some do not.

It is the Rad Alt signal that gets confused during heavy rain not WX.

Airbus brought out a FCOM Bulletin for A319/320/321 about this,

quote "Under heavy rain condition At 2600ft at least one of the radio altimeter delivered a height of 480ft during 13 seconds, The warning L/G not down was displayed"

Clearly this same phenomenon causes incorrect GPWS warnings also.

Of course, most of the above posts are also correct as I didn't specify my example applied to EFIS/FMS (Incl ex AA MD11) and certain manufacturers' GPWS systems.

For example, the Honeywell system GPWS/EGPWS as fitted on AA F-100's uses the radar transmitter/antenna for terrain mapping, along with the ppos database. If the wx radar isn't switched on and terrain selected ONLY the standard samplings i.e. VSI, rad alt etc. will provide warnings.

Other flight envelope samplings also occur depending on the aircraft's configuration.

For EGPWS on AA F-100;
turn Wx radar ON and push terrain button ON which, hopefully, turns a pleasant shade of blue. This is where the "signal" attenuation is sometimes mis-read and misinterpreted in heavy rain.

Radar alt on F-100 isn't "supposed" to work above 2500' agl.

However, along with the spurious GPWS warnings at 11,000' the rad alt can also read 1000' (in a nice green hue) in heavy rain. Honeywell is working on a fix at this time.

Cheers,

Yes, Dallas Dude
Question? Does the GPWS on the F-100 tell the crew to pull out or pull up?

Beleive we're getting a little confused about basic GPWS, the "Enhanced" EGPWS and the display systems needed to show the EGPWS terrain maps and visual alerts to the crew.

First, basic GPWS is not much more than a smart Radio Altimeter. The various other inputs, Baro Alt, Vertical Speed (= closure rate), flaps & gear only modify or even inhibit the "Pull Up" or "Terrain" calls. Radio Altimeters only read to 2,500 feet agl by design (as opposed to the high altitude military Radar Altimeters which go up to 50,000 feet or more). At 2650ft, they actually set "cruise mode" to avoid false indications.

Second, Enhanced or EGPWS always includes the basic function that must work independently and as if it was a GPWS alone (it's a requirement). EGPWS provides additional alerts by comparing aircraft height against a terrain database and Obstacles alerts by position & heading (the Obstacle must be within 4 degrees of heading to be shown if memory serves).

If a display is available, EGPWS will show a colour coded picture of surrounding terrain (if that display mode is selected by the crew). When they do this, they remove the WXR bus & replace it by the EGPWS data over a similar bus. This is why you have to have the WXR powered on some aircraft to get the display. Some aircraft also switch in TCAS the selection mix all on the MFD.

Well said ICT_SLB. With all the misinformation regarding avionics systems out there it's no wonder the most common phrase in the flight deck is "what's it doing now?" with the second being, "what's WHAT doing now?". Low Range RADAR altimeters-Geesh!

I have heard this EGPWS/radar theory before. Have seen it in action and have been given ground instruction on its operation and inputs, but, could it be that simple people like myself, jump to this conclusion when the EGPWS terrain depiction looks likes wx radar ground returns and are on the same sreen as wx radar returns.
Didnt know about rad alt being effected by wx, thanks will watch out for that.

In simple terms, GPWS uses the (downward looking ) Radalt to see how fast you are closing with the ground below and, depending on what stage of flight/configuration you are in, gives you a clue as to how to extricate yourself from the incipient mire. The EGPWS, however, uses the Radalt to see how fast you are closing with the ground below and, using the navigational accuracy of GPS and a digital database which gives it the contours of the ground ahead, can predict whether or not you will hit the ground ahead and will therefore know whether or not to serve you up an appropriate warning. Hence the various names given to EGPWS eg TAWS(Terrain Awareness and Warning System), Predictive GPWS etc.
With apologies to those more technically minded than me!
Cheers,
mcdhu

QNH1013
 

Flew in to Subic Bay a few times. There is extensive high terrain around the airport and the main approach is over the sea. Non Precision, VOR/DME approach and it is an Offset final approach course due to terrain anyway. At missed approach point or prior you are to be visial with the runnway and make final heading corrections to line up with the centreline.

Can't remember off hand what the MSA is there but there are 4 different high MSA altitudes centred around the Subic VOR. Any GPWS warning in IMC would be definitely well respected regardless of location anyway. But Subic is certainly a place to take not of the terrain even for the Missed Apporach procedures or you'll fly in to the side of a volcano. I'll post more accurate airport details when I look at the chart next time I'm at work.

6,800 is the worst MSA.

http://b757.users.btopenworld.com/SUBIC.jpg

Dallas Dude said;
If the wx radar isn't switched on and terrain selected ONLY the standard samplings i.e. VSI, rad alt etc. will provide warnings.

Most likely off on this one mate.
With the switch (terrain) off and radar off on
the 737, 757, 767, and 777's I'm flying the
database warning will
occur, aural that is. No time on the F100 but
that's the way the EGPWS is wired to the above
jets I've flown (AAL that is.)
Cheers, "California Dude"
:cool: