of the engine. If you toss in a hot start or an exceedance of the recommended operating temps, all things that can be within the pilot’s control, and the date with the maintenance department just got closer. How we maintenance folks deal with this begins
with trust. There must be a symbiotic trust between us and them (the pilots). When it comes to the helicopter, the pilots and us should be BFFs — best friends forever. Trust is like a three-legged stool. Every day the pilots trust that we have given them a safe helicopter as they play “you bet your life” with the helicopter we give them. That is the beginning ingredient or the first leg of the trust element. We trust they will return the helicopter in one piece, undamaged, and that the last whining we will hear is the turbine engine before it is shut down. That is No. 2. That now ends our trust in the pilot, right? Nope, not hardly. The third leg is communication between us and them. The pilots are our best troubleshooting tool and they need to understand and be comfortable with that. Who knows how that engine is running better than the pilot who has been working it for the last couple of hours? If we give them a little insight into what we need from them regarding engine operation and listen to them during the post-flight conversation, our jobs as rotor doctors (helicopter maintenance professionals) will be that much easier. Thus communication is the final ingredient to total trust. Here are some suggestions for information the pilot can provide: 1.) The engine idle temperature just prior to shut down. A rise in this temperature will indicate a probable cooling air leak.
2.) The engine oil pressure and temperature and any change to the steady state readings during flight and at idle.
3.) Any noticeable change in the vibration signature that they feel in the controls any time the engine is operating.
4.) Any possibility of a temperature exceedance either during flight or at start. Some helicopters have turbine temperature recording devices. I have always felt that this information was recorded not because the pilot can’t be trusted to report it, but because the pilots are usually pretty busy flying the helicopter and can’t always know exactly the length of time and the actual temperature that was reached at the time of an exceedance. This information is vital as the Ops & Maint manuals are very specific, meaning one second in duration and/or one degree of exceedance can make significant difference in the required maintenance and the cost of the repair.
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5.) Available power during flight. Was there a higher engine temperature required to achieve the same torque or power. How much? Perhaps the compressor needs a wash or there is some FOD or a malfunctioning bleed valve.
6.) What is the N1/Ng rpm during normal operation? They should know that this information is important to us. A change in N1/ Ng can be the harbinger of an eroded compressor or turbine.
7.) The other engine issue to which a pilot can be the contributor has to do with engine surging. I will explain more when we get to that section.
8.) Any abnormality in the behavior of the helicopter that the pilot notes is our responsibility.
HOT STARTS The pilot is in control of this event most of the time. I say most of the time because they are the ones controlling the fuel flow on the start, even in the case of engines equipped with full authority digital engine controls (FADEC). The pilots have the ultimate con- trol, or do they? A FADEC system has its own set of specific checks as does a conventional system and we won’t get into the particulars of either. Suffice it to say the items listed below are generic to all systems. Here are some items that are out of the pilot’s control: 1.) Has the helicopter just completed a maintenance event?
a.) Is the rigging correct? b.) Is the fuel control properly adjusted? c.) Are all the fuel system pneumatic lines tight and the system free from leaks?
2.) I s the battery fully charged? A low battery will not sustain the starter rpm through an entire start sequence, causing a hot start.
3.) Have the inlet covers been removed?
4.) A hot start requires accurate reporting from the pilot. As I said earlier, one second and/or a single degree will have a significant impact.
5.) Remember that damage from a hot start might be more noticeable downstream in the turbine. As the fuel/air ratio is out of balance, the flame will be seeking air further into the turbine section to sustain itself. Thus the tip of the flame will be moved from its normal location in the combustion section while it is searching for air and expensive turbine parts to sauté.
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