BAe 125 Series 800
Human-Machine Interface
Aircraft Equipment Problem Less Severe; Deviation / Discrepancy - Procedural Published Material / Policy
Flight Crew Overcame Equipment Problem; General Maintenance Action; General Release Refused / Aircraft Not Accepted
Company Policy; Aircraft; Human Factors; Manuals
I am writing this in response to something that has been bothering me for quite some time in the Hawker 800XPC/900XP fleet. This was further compounded by my experiences I had this winter. This has to deal with the TKS anti icing system on the Hawker 800XPC/900XP fleet. Starting last fall; I became very meticulous on verifying the TKS system on the airframe was working properly. In years past; I will admit that this was something I seldom checked and from my experience as flying quite a bit as a SIC due to seniority; other pilots neglect also. It seems that most assume it works and at a minimum just prime it once a day on the first flight for 2 minutes after Engine Start. However; after some feedback from other pilots and in one situation for myself where I was in flight and descending in icing conditions with the system primed for 2 minutes prior and it was running I was still getting some ice on certain portions of the TKS panels. I therefore started checking this system each time I picked up a plane.The first thing I noticed was that not a single plane would pass the TKS inspection on just running the system for 2 minutes. This number has been drilled into our head by [in training] as this is a requirement for priming prior to entering icing conditions. Therefore; I altered my procedure and used 5 minutes for my preflight check. What I still found was that on the planes that would eventually pass; I ended up having to do 2-3 cycles of 5 minutes to get good flow. However; I bet this winter I was only able to successfully get maybe 30% of the aircraft to pass and ended up MEL'ing the TKS system on these planes. At times I would run the system for as long as 30 minutes and would yet get flow on all the panels. Usually this system is seldom needed in the summer hence why I think most pilots never test it during preflight and just rely on the fact that it will work. However; when winter comes and this system is needed we then have more pilots but from my experience not all; testing the system hence the increase in write ups that seemed to have occurred with the TKS system this winter. Now I would like to speculate on why this problem is occurring. During my own research in this I had the pleasure of discussing this with some knowledgeable mechanics/pilots for some corporate flight departments that have operated the Hawkers for years. They all said that the system needs to be used year round. What happens is that once winter is past; the system is seldom used which leads to a multitude of problems with this system. These flight departments all have standard procedures requiring their pilots to use the system. As most of these operators go out and back from there base; it was very easy to use the system without depleting it before they get back to their base. They would also follow the AFM procedures recommendation of always priming 2 minutes after start; 30 seconds prior to climb; and 30 minutes top of descent and then would add the caveat to run the system during the final flight leg back to base for around 10 minutes so that they would try to time it so that after they landed and taxied in and the TKS timer would finish allowing them to check the system on post flight. By following these procedures; they stated that they seldom had problems with the TKS system which is a good thing because there is extensive maintenance work involved with this system as well as replacement cost associated with the panels. Now as it relates to my company; I would put forth that the biggest problem we have here is that pilots are not using the system as described in our Expanded Normal checklist procedures. When I look at our procedures; it states that the system should be primed at various times. Nowhere does it mention only if icing is suspected; but just the fact that it should be primed. It states this in the Preliminary-APU Start that the TKS system should be primed. It then states in the After Start that prime is required and this time for 2 minutes. It then states in a note in the Climb that the TKS system should be primed at the beginning of the climb for at least 30 seconds. Then finally on the Descent it states in a note that the system should be primed for 2 minutes. These steps laid out happen to mirror the AFM in the operations of this system. However; what my experience has been is that the standard tribal knowledge that prevails is that most just prime the system for 2 minutes after the first flight of the day and then don't touch it again unless icing conditions are encountered or until the next day the plane is flown and again only on the first flight for 2 minutes after engine start. Well during the summer the plane can easily never see icing conditions and combined with the plane sitting; that little 2 minute prime may not even be enough time to get fluid to even reach all the TKS panel let alone start flowing out the panel. I have witnessed this especially with the outward most panel on the wing as for whatever reason this takes quite some time to get flow out of it when the other panels are working properly. As for these procedures spelled out in the Expanded Normal checklist not being followed; I can only tell you what I have witnessed. As not every FBO offers TKS fluid; crews are more concerned with running out and limiting the availability of the airplane and will not use the system. However; since I have changed my technique and now follow the procedures as listed in the Expanded Normal checklist; even though my use of TKS fluid has increased significantly; I have yet to ever not be able to get it serviced before running critically low. I would also like to add that in all my line checks that I have had under the previous way I use to do the TKS system; not once did a line check airman ever point out that my limited priming of the system was contrary to the Expanded Normal checklist that even if you don't use the system you need to prime it more than just on the After Start on the first flight of the day. I describe all this as this is what I believe is leading to the high problem of the TKS system for the limited few of us pilots that check the system. I believe that this problem is much greater than being reported due to the fact that in my experience very few crews check the system properly. This added to the fact that in my experience; icing is very uncommon and seldom occurs even when in IMC below freezing. However; those times you do need it can be catastrophic if the system is not working properly. When I was experiencing my problems with the TKS system this winter; I was able to fly day with a Maintenance Check pilot and was able to discuss this situation with him. He was able to offer some more insight into this issue. For starters; he agreed that he also felt the biggest issue is that crews are not running the system enough and therefore causing the issue we have. But he went on to explain some more about the system. One thing he mentioned was that the system is designed to be run in flight and that by testing the system on the ground; the potential exist for the system not to prime properly especially if it has not been used enough. He went on to mention how the cold soaking of the plane and the colder temperatures and pressure acting on the wing aid in forcing the fluid to flow properly. He mentioned that his procedure and other Maintenance pilots is that when a TKS panel is removed; they prime the system for 10 minutes. However; rather than run the system for 10 minutes at once; they run it for 2 minutes 5 times. The reason for this is that in the first 2 minutes; the pump runs at a higher rate therefore the fluid is forced out at a greater rate aiding in the priming of the panels. Another thing he added was that if he does the TKS check and he doesn't get good flow which he feels is most likely cause by inadequate use of the system; he elects to fly a leg assuming the weather will not require the use of TKS for anti icing. What he does is he operates the system as prescribed in the Expanded Normal Checklist; 2 minutes prime/ 30 seconds climb/ 2 minutes top of descent but then adds that he runs the system for the final 12 minutes of flight trying to time it so that the timer quits as he is taxing into the FBO. He then can check the system on post flight and most times by doing this; even though he primed the system significantly on his preflight and it did not check; on post flight after using this procedure it has worked. After listening to all his input he added I decided to try this myself on the next airplane I encountered as long as the weather allowed for it. As typical on the next plane I encountered; after running the TKS for 15 minutes; I could not get the all the panels to flow properly. As the weather was VFR; I elected to fly the leg and ran the system as prescribed in the Expanded Normal checklist but also ran the TKS system for the last 15 minutes of the flight. On post flight; sure enough the panels were working properly. I had this plane for the rest of my tour and even though the weather never required the use of TKS; I ran the system as prescribed in the Expanded Checklist and never had a single problem with the system and I checked it on every preflight. The system worked flawlessly and further reinforced my belief that if the system is used continuously it works and primes properly. On the next tour I had a different airplane and proceeded to check the TKS panel. On this airplane after running it some 30 minutes; I was hardly able to get any fluid from most of the panels and then others flowed perfectly. As the weather was VFR; I elected to again try this new method of running it on landing. It ended up taking 3 legs but after the 3rd leg; the system was working perfectly. As the weather was VFR; it allowed me to do this instead of MEL'ing the system. I then proceeded to run the system every day and it always checked out every morning. This ended up really coming into play as my tours are 7 days and day 6; we flew into MDW. There was moderate icing at the altitude you had to be at for glide slope intercept. For a few aircraft that were departing and did not get a higher altitude; they were all experiencing moderate ice and were immediately requesting a higher altitude. As we were coming into MDW; we were forced to be at the prime icing altitude for some time as until we intercepted the glide slope and descended below it. As it was at night it was difficult to judge the ice accumulation on the non protected surfaces but after landing; we had about ½ inch of ice on the non protected surfaces. Fortunately our TKS system worked properly due to my checking of it and excessive priming of it; but I hesitate to think what could have happened to another crew who assume it would work and just turned it on 2 minutes prior to icing without having run the system of significant length for some time if it had not been operated in accordance to our procedures. On a final note; I would like to add one more thing that disturbs me. When I first started writing up the TKS system on the airplanes; I had some discussion with one of our maintenance controllers. This came about when I wrote up a plane that had various sections of certain TKS panels that would flow TKS fluid and other parts of the panel that wouldn't. When I came out to the plane the next day; the system was signed off as being fixed. However; when I primed it; I had the same thing. Over about 6 panels on the wing; some portion of the panels would flow TKS fluid but another portion would not. In discussing this with the maintenance controller; he sent me a copy of maintenance manual that describes the testing of the system. In the procedure; it states that a majority of the panel must work. Now the problem was what defines a majority? He was trying to lead me to believe that a majority could be defined as 51% and therefore if a panel is 4 feet long; as long as a majority
Hawker 800/900 Captain reports that the TKS deice system on his company's aircraft will rarely pass a preflight test on the first attempt; often requiring multiple attempts. He believes this is due to infrequent use and improper priming techniques.