F-18 Bleed Question

Bandit_Driver

Bandit_Driver

Gold Member
I was reading a military magazine talking about various mishaps in the military community and what can be learned from them. Anyways here's a brief excerpt and I am curious as to why resetting the bleeds is irrevocable action.

F-18 is out over the pacific refueling when the pilot gets and L BLEED and R BLEED warning followed by by L and R BLEED CLOSED. They disconnect from the tanker, pull green ring and descent to 10,000. They evaluate their status and may not have enough fuel to reach any divert point due to trapped fuel in the drop tanks. Then they were glad they could another tanker before they had to think about dropping the tank, resetting the bleeds or other irrevocable action.

So why is resetting the bleed bad JUJU in the F-18? Is there no procedure to isolate which engine the leak is on or isolate it. Can the bleeds not be closed again if manually reopened?

Thanks
 
Basically in the Hornet (that was a legacy jet, I don't know the specifics of the SH though I'd imagine they are similar) you have this thing called the BALD system......Bleed Air Leak Detection, which will sense if there is a bleed leak and automatically shut off the bleed air system (entirely so both L and R). Most guys that have Bleed Warnings only notice it for an instant if at all, because BALD will shut off the bleeds and you will be left with the bleed off cautions. It isn't possible to turn the bleeds back on if this has happened. If you manually shut them off, then you could certainly turn them back on. The real issue is that if there is a bleed air leak, you are going to have a fire in pretty short order......all that extremely hot air getting blown into places it shouldn't be.......makes for what we call a keel fire, or a fire in the back of the jet between the motors in the "keel" section. For the sake of the discussion, it is often a worn out bleed air line part called the S-bar. I don't know what it is made of, but it looks plastic, and they get worn out and cracked after years of being in a pretty hot environment. I don't actually know what function it serves, but I know that it is normally preceded by months of gripes about excessively hot cockpit temps and other weird ECS issues. Then it just blows and you get a bleed air warning and then they fix it :) You can definitely have an isolated L or R bleed warning/caution, in which case the procedure does not involve shutting off the entire bleed air system unless going L/R bleed off doesn't stop the issue. I don't remember the specifics of that article, but the big issue you have with the bleeds secured is that you can't transfer external tank fuel, and you don't have pressurization, both things that would be a big issue on an overwater ferry flight. For what it is worth, the guy flying who wrote that article was a RAG buddy of mine from Miramar. Real smart guy.
 
Thanks AMG...seems like a good idea on paper but you'd think they'd (Boeing) let a pilot override the system, if the risk of fire was the lesser of two evils.

I'll see if I can find the article again and post it.
 
Bandit_Driver said:
Thanks AMG...seems like a good idea on paper but you'd think they'd (Boeing) let a pilot override the system, if the risk of fire was the lesser of two evils.

I'll see if I can find the article again and post it.
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Should be on the Naval Safety Center website under approach magazine....they are all downloadable.

To be honest, I can't think of a scenario where I would ever turn bleeds back on if I had a leak. It isn't a question of if you will have a fire, but rather how soon. Obviously there could be a scenario, but I can't think of it. A bleed warning is one of the more serious "I need to get on a piece of pavement right now" emergencies that we have. Engine fire, bleed warning, mech reversion (a result of a complete FCS failure), and maybe an afterburner blowout or engine failure (depending on my max abort airspeed on the given day) are about the only things I will high speed abort for because they are serious enough that I would rather risk blowing tires/going off the runway/ejecting than take the thing flying.
 
That was the magazine...article starts on page 30

http://www.public.navy.mil/navsafecen/Documents/media/approach/2013/AppMar-Apr13.pdf



It's obviously a different bleed system than I have ever had experience with. Everything I have flown allowed us to turn them on/off at will and numerous ways to isolate a leak, up to and including just shutting down one engine if the leak couldn't be isolated at various points. The only one on the 727 what was super serious was a lower aft body over heat (keel beam). If you couldn't isolate it fast, it was a we needed to be on the ground 10 minutes ago situation because the plane will literally break apart in flight once the keel beam melts.

hypothetical: if one were able to force the bleeds back on couldn't he have use them to transfer the fuel from the drop tanks to the internals or does the F-18 have small internal tanks thus the reason for fuel still being in the drop tanks...
 
Let's also remember the primary purpose for an aircraft like the Hornet: to be a vehicle in which a single individual can use a multitude of different weapon systems to achieve a combat goal.

So, there is a human factors engineering root to system designs like this. It is with those human factors in mind that decisions like automating the bleed air control decisionmaking if there is a failure in the system are made. Both the fact that it is a single individual in the aircraft, AND that it is a high performance combat aircraft, are going to seriously influence how in-depth any kind of manual analysis and/or troubleshooting is possible or allowed. Also remember that simply "flying the aircraft" is only about 10% of a fighter pilot's cognitive task load -- the other 90% is mission-related tasks, like weapon system operation and interpretation, tactics execution, etc.

Remember that an airplane like the 727 had a dedicated FE in the mix when it was designed; the capabilities so far as finding complicated system problems and making specific decisions about how to fix those issues are going to be much more detailed because there is a specific person whose job it is to do that, and who is not also responsible for manipulating the controls and flying the aircraft.
 
Bandit_Driver said:
It's obviously a different bleed system than I have ever had experience with. Everything I have flown allowed us to turn them on/off at will and numerous ways to isolate a leak, up to and including just shutting down one engine if the leak couldn't be isolated at various points. The only one on the 727 what was super serious was a lower aft body over heat (keel beam). If you couldn't isolate it fast, it was a we needed to be on the ground 10 minutes ago situation because the plane will literally break apart in flight once the keel beam melts.

hypothetical: if one were able to force the bleeds back on couldn't he have use them to transfer the fuel from the drop tanks to the internals or does the F-18 have small internal tanks thus the reason for fuel still being in the drop tanks...
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Just like Hacker mentioned, we just don't really spend a lot of time troubleshooting systems airborne. The sim guys in the RAG love to throw crazy unrealistic compound emergencies at you, but in real life, normally it is a matter of getting through the boldface and getting the thing on deck as soon as you can. We have 8 circuit breakers in the cockpit, and 4 of them are for the flight controls. I'm not saying there aren't times when you need to troubleshoot airborne, but the 90% solution is shutting down whatever is messed up, and then landing, and not wasting a lot of time and running out of gas trying to figure out what is going on.

As for your hypothetical, with double bubble/double ugly/etc (2 drop tanks) the most you are going to have is about 4400 lbs of trapped fuel if you can't transfer, and probably a lot less than that since the externals transfer first (unless you are unlucky and they don't transfer from the get go, or in this case, you are tanking for a long distance). So it generally isn't really a consideration. You can still get pretty far on internal fuel, and unless you are blue water (no divert), you can likely land. That is provided you realize that you have trapped unusable fuel. I actually had a centerline today that would not transfer its last 1000 lbs. Not a big deal, but it would have been a big deal had I not knocked the mission off 1000 lbs early realizing that those were 1000 lbs I wasn't going to be able to use. Anyway, long explanation, but the bottom line is that I am not going to risk a fire just to transfer how ever many hundreds of lbs are still in the tank(s).
 
Great points. I can definitely see the differently thinking now in the design of fighters and crews. You only fly one side of aviation you get stuck thinking one way.

Thanks...
 
Bandit_Driver said:
Great points. I can definitely see the differently thinking now in the design of fighters and crews. You only fly one side of aviation you get stuck thinking one way.

Thanks...
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Oh don't get me wrong, I agree completely. My perspective on a lot of nuances is probably wildly different than any of you guys flying the heavy metal. I would be a scared fish without fins if I just hopped into your shoes for a day, at least judging by a lot of the shop talk around this forum and others. I think most all of us can see the fundamentals through a similar light, but the specifics, norms, standards, etc are very different between the various communities out there. I'd even say in a micro sense, we do things noticeably different than AF fighter guys, or even our own tacair non-Hornet types. Hell, I can't even get a Rhino to administratively lead me to and from the area at any less than 9000 knots (unless you count the random fluctuations to -100 knots because they haven't learned to find the autothrottle function of their jets) :) . They just don't have to worry about fuel like we do. Even those little things make a big difference in mentalities.
 
No worries ///AMG, all good here.

Slightly off topic warning:

So with the Rhino's increase fuel capacity and weights approaching that of the F-14 does it handle like a dog? What's your opinion of the Navy putting all their eggs in one basket with the F-18's. I understand the cost side of it, but if you make a plane a jack of all trades can it excel at any of them. I with they would find a way to build the Tomcat again using modern technology...
 
When I was in, they were trying to make the Tomcat's more like the Hornets.

We had the "Bombcat" program, adding software mods to make the Tomcats attack birds. Pretty silly with the amount of available weapons stations capable of carrying ground attack munitions on the F-14 (Unless you can fit it in the Phoenix conformal :) )

What's nice with the Rhino is it has some bring back capability, 10k if I remember right. No more dumping good weapons in the water.

Rhino has a much lower empty weight than the 14, but gross should be slightly more capable.
 
Yeah bet dumping good weapons in the water has to be pretty frustrating for all involved

I am also guessing the Phoenix missile is now useless that the tomcats are gone. IIRC only the F-14 could carry it.
 
Bandit_Driver said:
I am also guessing the Phoenix missile is now useless that the tomcats are gone. IIRC only the F-14 could carry it.
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Well Iran still has F-14 :)

It was a good weapon against long range, non maneuvering targets, like the Bear and Badger. It was a burn and glide weapon.
 
Didn't know that. I thought he Phoenix was fire and forget and it tracked well.

I know Iran still has them which I heard is why ours were so well destroyed and one wasn't given to the Collins Foundation. We didn't want any parts making their way over there..
 
Bandit_Driver said:
Didn't know that. I thought he Phoenix was fire and forget and it tracked well.

I know Iran still has them which I heard is why ours were so well destroyed and one wasn't given to the Collins Foundation. We didn't want any parts making their way over there..
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It is Fire an forget and does track fairly well, it just doesn't have energy at the end of cruise to turn with a fast mover.

They also have a 747 tanker we made for them years ago. We had our RARO demonstrator at the Dubai Air show around 2003 or 2004 and some Iranians approached our guys and talked for a bit. They told them they had the 747 Tanker working again.....Pissed off our crew as they had to debrief the whole thing when they got back :)
 
Damn that sucks. I've hear debriefings suck. I would imagine they are pretty creative at fixing things and I wouldn't be surprised if they have been making their own parts and patching the crap out of the f-14's
 
I have had the opportunity to speak to some active Iranian Air Force guys in the last couple of years. They told me that the Tomcat is used primarily as a theater AWACs aircraft, despite efforts to keep the Phoenix operational. I'm not sure of the status of the program, but they were experimenting with arming their Tomcats with modified Hawks.
 
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