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Pac 750 stalls on jump run

 

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skyjumpenfool  (Student)

Jun 15, 2009, 9:05 AM
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Pac 750 stalls on jump run Can't Post

Saturday June 13th, 2009 Waseca, MN
PAC 750XL flying 13 skydivers (12 way w/camera) stalled on jump run w/several jumpers hanging outside the aircraft at 13K. The jumpers outside the plane were pealed from the plane and all the jumpers inside were able to get out. The pilot did a nice job of recovering from the stall. No one was injured and to my knowledge no damage was done to the aircraft. However, with the growing popularity of the PACs in this sport, I think this incident needs to be discussed.

The pilot and DZ management took the incident very seriously. Much was discussed and pictures were taken of the jumps exit order etc.

The video shows very little of the stall, except for the horizon disappearing from the frame. There were very experienced jumpers on the load along with a commercial pilot/jumper. So, IMHO, theres much to be learned from this incident.

On a subsequent 13 way, jump run speed was noticeably increased.


jakee  (C License)

Jun 15, 2009, 9:19 AM
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Re: [skyjumpenfool] Pac 750 stalls on jump run [In reply to] Can't Post

How many jumpers were floating and in the door? Did the late divers make sure they were as far forward as possible? CoG is really important when you're taking a big group out of a PAC...


JohnRich  (D License)

Jun 15, 2009, 9:21 AM
Post #3 of 110 (5961 views)
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Re: [skyjumpenfool] Pac 750 stalls on jump run [In reply to] Can't Post

In reply to:
On a subsequent 13 way, jump run speed was noticeably increased.

It would be nice if you would publish here those two parameters: 1) What speed was "too slow", and; 2) what speed was "just right".

With the increasing popularity of this jump plane, the skydiving community needs to know what it takes to safely launch big-ways from them.


GLIDEANGLE  (D 30292)

Jun 15, 2009, 9:22 AM
Post #4 of 110 (5958 views)
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Re: [skyjumpenfool] Pac 750 stalls on jump run [In reply to] Can't Post

The title of this thread is unfortunate. It implies that the aircraft was the culprit. There are at least three key elements which play roles:

-- Pilot
-- Jumpers
-- Aircraft

Each is important and needs to be considered when thinking about an incident like this.


davelepka  (D 21448)

Jun 15, 2009, 9:37 AM
Post #5 of 110 (5929 views)
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Re: [skyjumpenfool] Pac 750 stalls on jump run [In reply to] Can't Post

Quote:
There were very experienced jumpers on the load along with a commercial pilot/jumper.

There are several factors that make these points moot.

If the very experienced jumpers are floaters, then the less experienced divers may not know that they should not crowd the door, and remain forward in the AC until the exit has begun.

Even if the more experienced jumpers are divers, if the bigger jumpers in the group are floaters, this adds more weight to the tail, and more drag outside the plane. Even with the divers well forward, the big boys can drag the tail down.

Regradless of the pilots experience, if he is not informed that the entire plane is one group, then he may not be ready for the amount of weight that will be shifting rearward. If a pilot is flying back to back loads and not present for the dirt dive, or not a jumper not aware of the dirt dive, then they will have no cause to alter their jumprun procedure.

Anytime there is a bigger or heavier group exiting the plane, the pilot should be informed and few extra knots on jumprun should be requested. We have several jumpers at my DZ who are 250 lbs +, and they tend to jump together. I make it a point to inform the pilot that he'll have 1000 or 1200 lbs hanging outsdie of the plane on jumprun on that load, and he'll keep the speed up accordingly.

One last point in looking at this problem is the jumpers themselves. It's important to make sure they know and understand the concept of aft CG, and stalling on jumprun. They should be able to recognize the situaiton, and realize that they need to contribute to the recovery by letting go of the plane.


pilot-one  (D 30000)

Jun 15, 2009, 9:53 AM
Post #6 of 110 (5908 views)
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Re: [skyjumpenfool] Pac 750 stalls on jump run [In reply to] Can't Post

An airplane can stall at any speed depending on several variables. It amazes me how many pilots are surprised their aircraft stalls at a substantially higher speed than the published speed in the POH. Ultimately it is the pilot's responsibilty to keep the aircraft flying.
With my 5000 hours of flying heavy loads in the bush of Alaska and the limited information provided, I would call this pilot error having nothing to do with the design of the airplane itself.
Obviously this pilot realized his mistake and made the appropriate adjustment on the next jump run. Good for him.


kallend  (D 23151)

Jun 15, 2009, 11:42 AM
Post #7 of 110 (5831 views)
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Re: [JohnRich] Pac 750 stalls on jump run [In reply to] Can't Post

In reply to:
In reply to:
On a subsequent 13 way, jump run speed was noticeably increased.

It would be nice if you would publish here those two parameters: 1) What speed was "too slow", and; 2) what speed was "just right".

With the increasing popularity of this jump plane, the skydiving community needs to know what it takes to safely launch big-ways from them.

Every Skyvan I've jumped has had lines in the cabin indicating "only X jumpers rear of this line" (or similar, etc.). If the PAC really is susceptible, maybe it needs some similar marking.


SARLDO  (B 31063)

Jun 15, 2009, 12:01 PM
Post #8 of 110 (5797 views)
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Re: [kallend] Pac 750 stalls on jump run [In reply to] Can't Post

I thought the PAC has a very wide Leading Edge Mean Aerodynamic Cord (LEMAC) and not easially put out of CG without heavy cargo on board and aft.

I have a few PAC jumps and seen many (big) jumpers crowding the door/outside. Pretty slow jump run speeds and no indications of stall.

Airspeed is life...


skyjumpenfool  (Student)

Jun 15, 2009, 1:13 PM
Post #9 of 110 (5753 views)
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Re: [davelepka] Pac 750 stalls on jump run [In reply to] Can't Post

In reply to:
Quote:
There were very experienced jumpers on the load along with a commercial pilot/jumper.

There are several factors that make these points moot.

My point in posting this was to have a well needed discussion. My reason for pointing out that there were experienced jumpers is that they will have valuable insight to share. And, hopefully, they will share.

Let's not look for fault here. Rather, let's share info and discuss how to avoid this situation in the future.


kelpdiver  (B 7)

Jun 15, 2009, 1:38 PM
Post #10 of 110 (5724 views)
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Re: [skyjumpenfool] Pac 750 stalls on jump run [In reply to] Can't Post

When the PAC first showed up in the US at Skydance, I believe the jumpers managed to create a similar situation. So this shouldn't be a total surprise. The plane is pretty friendly, but still has limits.

How many are in the US now? Hopefully those pilots are comparing notes and making sure the information gets to jumpers.


Fast  (D 28237)

Jun 15, 2009, 1:55 PM
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Re: [skyjumpenfool] Pac 750 stalls on jump run [In reply to] Can't Post

How many people were outside the plane? From practice I have found that a practical number of people outside doesn't really coincide with the number of people who actually fit out there.

Been there, done that, didn't like it and learned from it.


Sletzer  (B 31200)

Jun 15, 2009, 1:56 PM
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Re: [kallend] Pac 750 stalls on jump run [In reply to] Can't Post

Casas are the same way with the lines that say "X number of people past this line." I do agree with what was stated earlier that with newer jumpers (myself included), the more experienced people sometimes need to remind the divers to stay towards the front of the plane. That being said, if the floaters feel the plane start to stall, they should just let go.

On a side note, last time I was in a PAC, the stall warning went off probably 7 times while climbing because the pilot was apparently in a hurry and climbing too steeply. Our 8 way sure didn't dick around in the door once at altitude, and someone brought it up with the pilot afterwords.


davelepka  (D 21448)

Jun 15, 2009, 2:19 PM
Post #13 of 110 (5666 views)
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Re: [skyjumpenfool] Pac 750 stalls on jump run [In reply to] Can't Post

Quote:
Let's not look for fault here. Rather, let's share info and discuss how to avoid this situation in the future

It's interesting how you selected one line of my post, made in bold print, and responded as if that was my entire post.

I'm pretty sure that if you read the rest of my post, it is directed squarely at the situation you described, the errors that may or may not have contributed, and some additional points intended to prevent this same situation from repeating itself.

To more directly respond to your follow up post, you stated that experienced jumpers were on board, and that the pilot was also a jumper, and I wanted to point out that the presence of these people does not guarantee that these types of things will not happen. Unless specific, proactive steps are taken (such as informing the pilot of the intended exit plan, and making sure divers know to stay forard in the plane) then you cannot assume that just because certain people have certain qualifications that things will go smoothly.

Let's remember that there are a fair number of low time jumpers who read these forums, and that information should be presented in a complete and thourough manner. To assume that anyone 'knows' one thing or another would be making a mistake, a bigger mistake in my opinion than including too much detail or information.

I'm not sure why you want to avoid finding fault. The stall did not occur by itself, it was the result of human action or inaction. The only way to prevent is to fully understand the actions and circumstances that led to the problem, and avoid them in the future.

I would hold the pilot responsible for not maintaining sufficient airspeed. I would also the jumpers responsible for contributing to the stall by not informing the pilot of an exit plan that would be a deviation from the normal jumprun, and that could effect the CG of the airlpane.


skyjumpenfool  (Student)

Jun 15, 2009, 2:43 PM
Post #14 of 110 (5637 views)
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Re: [davelepka] Pac 750 stalls on jump run [In reply to] Can't Post

In reply to:
It's interesting how you selected one line of my post, made in bold print, and responded as if that was my entire post........

Agreed! But let me clarify a few points...

1) One of the jumpers, the one nearest the front of the aircraft, is also a commercial pilot. He would have much to share here. And those who know him respect his opinions. I don't know if the pilot is also a jumper??

2) All on the load were to exit together. 12-way RW plus 1 camera man (myself). So, all were crowding the door.

3) I don't know the exact airspeeds. But, it was very apparent that, on a later dive, the pilot made a correction and the airspeed was noticably higher.

There were 12 other folks on this load who have a version of this story that I would like to see shared. Also, I'm hoping the pilot is willing to talk.

When the aircraft stalled, I (rear float w/camera) was very nervous about the tail. It didn't seem to play into this scenario.


davelepka  (D 21448)

Jun 15, 2009, 2:56 PM
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Re: [skyjumpenfool] Pac 750 stalls on jump run [In reply to] Can't Post

Quote:
All on the load were to exit together. 12-way RW plus 1 camera man (myself). So, all were crowding the door.

I fully understood all of this from your first post. However, just because you're doing a 12 way, that is no reason to crowd the door.

Figure if you have 4 or 5 floaters, and you can squeeze another 3 drectly in the door inside the plane, that leaves at least 4 or 5 jumpers who will be nowhere near the door. These jumpers can remain forward in the plane during the climbout.

There's nothing they can do until the jumpers inside the door leave anyway, so until those jumpers begin to move, the divers can stay forward. With a left side door, have the divers line up single file along the right side of the plane. When the door is clear, they can single file it right out of the door.

This is basic organizing, and something the oragnizer of this dive should have set up. This alone would have put 1000lbs further up the cabin, and from the looks of it, over the wing itself, as opposed to behind it.

The organizer should have also communicated the situation to the pilot. The more weight you put it the back of the plane, the more elevator you need to keep the tail up. The slower you fly, the less control authority you have, so adding a few knots would have given the elevator a lttle more 'power' and possibly kept the plane flying.

Addionally, if you have too many floaters outside the plane, especially in a low-tail plane like the PAC, those jumpers create a burble which may blanket the left side of the tail, further reducing it's effectiveness. Again, more speed would provide additional airflow, and additional control authority.


sdctlc  (D 16437)

Jun 15, 2009, 3:00 PM
Post #16 of 110 (5613 views)
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Re: [skyjumpenfool] Pac 750 stalls on jump run [In reply to] Can't Post

In reply to:
2) All on the load were to exit together. 12-way RW plus 1 camera man (myself). So, all were crowding the door.

<snip>

When the aircraft stalled, I (rear float w/camera) was very nervous about the tail. It didn't seem to play into this scenario.

As has been stated, you can stall any jump plane given the right circumstances.. Even the trusty Otter can get got if your doing just the right (wrong) things. I have been on numerous loads with 20 ways where we hold back the last 4-5 or even 6 jumpers in the formation, back up near the Pilot. When they see the outside floaters and the chunk start to go they quickly move to the door. Basically as they are moving towards the door they most likely are right with the divers leaving just in front of them giving no real delay or gap if it is done right. This takes a good bit of the aft weight away helping with the CG.

With only a few jumps out of a PAC personally, I am guessing it was not a 12 way chunk and keeping a few jumpers up towards the spar "hump" up closer to the pilot would help on CG while not hurting exit speed.

Just a thought. Maybe one of the jumpers that does more RW at a PAC DZ can chime in..


rehmwa  (D 12816)

Jun 15, 2009, 3:28 PM
Post #17 of 110 (5575 views)
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Re: [davelepka] Pac 750 stalls on jump run [In reply to] Can't Post

In reply to:
This is basic organizing, and something the oragnizer of this dive should have set up.

Dave - you nailed all the key points, can't figure out your tone though.....

You have about 3 'shoulds' here for the organizer, all were done prior to the jump other than we had one more person out. You have a couple "shoulds" for the pilot - those were ID'd in the post brief and they worked fine for the rest of the boogie.

I was the organizer:

1 - line up was equivalent to an 8-way chunk + camera, something we've done on our local PAC repeatedly with no issues

2 - the other 4 jumpers were to line up forward (to the front of the plane, but in the aisle) and be ready to move on set

3 - the pilot was informed prior to the jump (I did it personally) that this was a single group with a big climbout. As the plane was also turning all day, he had a lot of other stuff to process through the day. I believe on this load, he followed the procedure on this jump that the owner gave him for all the jumps runs.

4 - We had a few very heavy jumpers outside - I'd line them up differently for more margin if I were to do it again (despite the below corrections). 3 were particularly big guys.

5 - typical stall, very nose high and then rolled to port - the pilot handled the stall perfectly

6 - the pilot came to the ground and was only interested in how the plane was configured and how he could fly that type of lineup better - a super professional guy and he and the jumpers were very good about lessons learned. He reviewed it with myself and the pilot of our group (jump pilot also) and all agreed that more speed is the key on this situation. I decided to adjust the lineup as well going forward to help on 9+ groups, but the other two thought that wasn't necessary - though appreciated

7 - later jumps - with the correction had absolutely no issues, and the 'feel' of the jump run was that the tail was absolutely locked 'up' on jump run despite any combo of 'beef' on the loads.

FYI - I'll check in here and answer any questions as long as people stay courteous.


rehmwa  (D 12816)

Jun 15, 2009, 3:33 PM
Post #18 of 110 (5567 views)
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Re: [davelepka] Pac 750 stalls on jump run [In reply to] Can't Post

In reply to:
To assume that anyone 'knows' one thing or another would be making a mistake, .............
.
.
.I would hold the pilot responsible for not maintaining sufficient airspeed. I would also the jumpers responsible for contributing to the stall by not informing the pilot of an exit plan that would be a deviation from the normal jumprun, and that could effect the CG of the airlpane.



Since you weren't actually on site, best you 'know' some details:

1 - the pilot. If he were to choose to be on site here, he can address that himself. I think he did a very good job both in handling the stall, and making a change after to avoid it again

2 - the jumpers. as noted, we let the pilot know of the load size before boarding


Premier PhreeZone  (D License)
Moderator
Jun 15, 2009, 6:26 PM
Post #19 of 110 (5493 views)
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Re: [rehmwa] Pac 750 stalls on jump run [In reply to] Can't Post

Quote:
2 - the jumpers. as noted, we let the pilot know of the load size before boarding

One thing that I've found helps the pilot out a lot is to pass the word back to him/her as a reminder at about the 2/3's way mark (8-9000 feet) about the more unusual exits since they have had 10-15 minutes full of other activities that they have had to do and this bit of info might have slipped the top of their mind. Especially if it is a busy day and the loads are really turning its easy for everyone to get distracted and a bit of a reminder helps a lot to keep important things like that at the top of the pilots mind.


rhys  (D 95)

Jun 15, 2009, 7:11 PM
Post #20 of 110 (5460 views)
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Re: [skyjumpenfool] Pac 750 stalls on jump run [In reply to] Can't Post

Obviously it is hard to know from this conversation what actually caused this to happen but I have been told by pilots that have lots of time in crescos and XL's that if there are too many people outside, they can steal the airflow off the left hand horizontal stabaliser, so with correct trim, airspeed, and centre of gravity the palne can still dip/stall to the left beacuse the stabaliser on the left isn't working anymore.

Keeping chunks and floaters nice and tight to the fusilage helps rather than hanging right out looking for the cadence, espacially big tall guys.

The XL is not perfect for big ways in that respect but its economical advantages outweigh that disadvantage for the owner.


davelepka  (D 21448)

Jun 15, 2009, 7:41 PM
Post #21 of 110 (5438 views)
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Re: [rehmwa] Pac 750 stalls on jump run [In reply to] Can't Post

Quote:
2 - the jumpers. as noted, we let the pilot know of the load size before boarding

Thank you for posting the details of the situation. I know that I listed several responsibilities the jumpers/organizers have in a situation like this, and from what you've mentioned, they were all met.

I was laying out the different possibilities for how the type of situation could transpire. I wasn't suggesting that all of them occured in this instance, but that these were the things to consider when going into a similar situation.

In terms of the pilot, while he is responsible for maintaining sifficient airspeed, in no way was I suggesting that he was sloppy, or intentionally let the stall occur.

You mentioned that the base was an 8-way chunk in the door, and that you had done this exit many times in your 'regular PAC', leading me to believe that this was not your 'regular PAC' nor was it the pilot you were used to. This comes back to the idea of not assuming that anyone just 'knows' anything.

Through no fault of his own, and like many jump pilots, he may not have any experience with groups of that size out of that plane. Even a high-time jump pilot may have spent 80% of that time in a 182, and 20% in a turbine at a DZ where the turbine only flies when there are tandems on board (limiting the size of the RW groups, and number of people in the tail).

It sounds like the pilot reacted the right way during the stall, on the ground afterwards, and on subsequent jumpruns, and that's all you can ask of him. As a pilot he has no say over what type of experince he'll have during jump operations, that's simply a function of where and who he's been flying. Mistakes do happen, but by handling it properly, and using it as a learning experince, he's just become that much better at flying jumpers.

Again, between you, me and some of the other more experienced jumpers on here, what I'm saying is old news, but for those who are hearing about this for the first time, I'll include the details of how and why things work the way they do.


JohnMitchell  (D 6462)

Jun 15, 2009, 8:41 PM
Post #22 of 110 (5389 views)
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Re: [Sletzer] Pac 750 stalls on jump run [In reply to] Can't Post

In reply to:
On a side note, last time I was in a PAC, the stall warning went off probably 7 times while climbing because the pilot was apparently in a hurry and climbing too steeply.
Stall warnings sometimes go off intermittently on turbulent days. Was that the case?

If the pilot really was just flying at a higher angle of attack in an attempt to climb faster, he is not a very bright or good pilot. Planes have a certain best-rate-of-climb speed for a given gross weight, and it's rarely at a speed that gives an angle of attack close to stall. Higher AOA means more induced drag, less power for the climb. Ask your pilot what his best rate of climb speed is for a full load.


virgin-burner

Jun 16, 2009, 2:15 AM
Post #23 of 110 (5349 views)
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Re: [kallend] Pac 750 stalls on jump run [In reply to] Can't Post

In reply to:
In reply to:
In reply to:
On a subsequent 13 way, jump run speed was noticeably increased.

It would be nice if you would publish here those two parameters: 1) What speed was "too slow", and; 2) what speed was "just right".

With the increasing popularity of this jump plane, the skydiving community needs to know what it takes to safely launch big-ways from them.

Every Skyvan I've jumped has had lines in the cabin indicating "only X jumpers rear of this line" (or similar, etc.). If the PAC really is susceptible, maybe it needs some similar marking.

with ours, the rule is no more than 5 jumpers in/outside the door, rest of the load BEHIND (actually in front) of the door. no exclamations!


rehmwa  (D 12816)

Jun 16, 2009, 6:45 AM
Post #24 of 110 (5271 views)
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Re: [davelepka] Pac 750 stalls on jump run [In reply to] Can't Post

Thanks, Dave - I'm always a bit leary of threads like these, they tend to degenerate quickly

Quote:
from Rhys - floaters nice and tight to the fusilage helps rather than hanging right out

this is an interesting point, since the door of the PAC is so small (vs an Otter) I like to have the floater across from the inside rear (for an 8 way chunk) hang away from the plane to let that inside rear get their shoulders out to make room for the other inside people (always hard to get them to line up correctly anyway) - this is a conflict to protecting the flow around the rear low stabilizer - should be small unless we have too many huge skydivers

best solution, only use small skydivers Shocked


(This post was edited by rehmwa on Jun 16, 2009, 10:35 AM)


skyjumpenfool  (Student)

Jun 16, 2009, 1:55 PM
Post #25 of 110 (5168 views)
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Re: [rehmwa] Pac 750 stalls on jump run [In reply to] Can't Post

It would be good to point out also that on this load, one of the floaters is a very big guy. And, the video pointed out that he and the front floater were very high on the step. They were probly creating quite a burble for the horizontal stabilizer.


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