Small Transport; Low Wing; 2 Turbojet Eng
Flight Crew Instrument; Flight Crew Multiengine; Flight Crew Air Transport Pilot (ATP); Flight Crew Flight Instructor
Flight Crew Last 90 Days 49; Flight Crew Total 4415; Flight Crew Type 1550
Time Pressure; Workload; Communication Breakdown
ATC Issue All Types; Aircraft Equipment Problem Less Severe; Conflict Airborne Conflict; Deviation - Altitude Overshoot; Deviation - Altitude Excursion From Assigned Altitude; Deviation - Altitude Crossing Restriction Not Met; Deviation / Discrepancy - Procedural Published Material / Policy; Deviation / Discrepancy - Procedural Clearance; Inflight Event / Encounter Weather / Turbulence
Flight Crew Overcame Equipment Problem; Flight Crew Returned To Clearance
Aircraft; Weather; Human Factors
The Deviation event occurred over or around the HLMET intersection on the LDA Runway 35 approach into Salt Lake City International. ATC instructions were to proceed direct to HLMET; Cross HLMET at 11;000; cleared for the approach. Somewhere just seconds before or after crossing HLMET I descended to an altitude of approximately 9;600 MSL. The altitude on approach after crossing HLMET is 10;000 MSL until crossing the nest fix PEDLE. However after becoming distracted (which I will explain later); I noticed my altitude got down to that approximately 9;600 MSL for which I knew was not right; and immediately began corrective action while simultaneously ATC queried my altitude and I made mention of correcting. I saw I was just passed HLMET and quickly climbed back up to the crossing altitude of 10;000 MSL. Shortly later the controller mentioned the possible pilot deviation may have led to a loss of separation; although no TA/RA's were issued by either aircraft. Here is where I want to bring to attention the possible safety issue as related to the situation and what resulted in me becoming distracted and task saturated. Starting at an ATC controller back before TRACON; which was Salt Lake Center and while on the QWENN 5 RNAV Arrival off the MLF VORTAC transition; I was left extremely high by the center controller; for which I was expecting to receive the 'Expect' crossing restriction at FRNZY intersection at 15;000 MSL on the chart. I could hear multiple aircraft in front of me getting the FRNZY at 15;000 MSL restriction; but also complaining of being left very high and possibly not being able to make it. As I started to see the FMS computer show a required 3;500 FPM decent to make that restriction; I thought I better ask the controller for a descent; however the frequency was congested and it took many more minutes until finally the controller just issued me to now cross FRNZY at 16;000 MSL and 250 KTS. I replied that I would do by best; but it would be tight to make. Mind you that this new altitude required my attention to reprogram the altitude into the FMS as I anticipated and setup for 15;000; and still it showed a required 3;800+FPM decent to make it. I immediately initiated the decent for which I used the VNAV mode in the FMS/autopilot to make the crossing; which also required idle power and the activation of the aircraft's speed brake system to induce drag to not over-speed in the decent. During the decent on the arrival there was also light to bordering on moderate rime icing in IMC and snow showers. When the engines are at idle power they do not produce enough bleed air to keep the Anti-Ice/De-Ice systems operating; for which I got warning that they were not being kept hot enough; so I was trying to introduce small amounts of power to try and get more bleed air flowing to those systems; all the while trying not to over-speed and setup for the instrument approach. Being single-pilot this induced a very high work load; which caused me to become task saturated and behind on preparing for the approach. After finally passing FRNZY at the 16;000 MSL altitude and still in icing conditions and IMC I was simultaneously passed to TRACON approach control which issued me the direct HLMET; cross at 11;000 MSL; cleared approach restriction. I continued the decent down out of 16;000 MSL to 11;000 MSL still using VNAV on the autopilot (more on that later). I noticed I was still nearing around idle power and adding what I could but was still having trouble keeping the speed under control and still behind on setting up the approach. Somewhere around 12;000 MSL I got an indication that the speed brake panels went down; even though I didn't select it. Wondering what happened I looked out the pilot side window at the wing and noticed they were in fact still up; just no longer indicating it in the cockpit. This distracted me; as I knew I needed them extended to maintain my speed and help to try and keep power up and bleed air flowing. It took mybrain a few moments to try and figure out what was going on as there is no abnormal procedure for that in the checklist. I decided to recycle the speed brake switch; for which they then operated normally (retracted and extended); and then gave all normal indications. Throughout that situation is when the altitude deviation occurred; as after I was confident there was not a problem with the speed brakes and they just needed a reset; I accidentally went through the 11;000 MSL attitude down to the approximately 9;600 MSL altitude. Upon speaking with Maintenance later on the ground they feel that the system was activated for so long throughout the decent continuously; they work trapping hydraulic pressure to hold it up; that logically that pressure must have bleed down some; causing them to blow in-trial/down just enough to give an indication in the cockpit that they were sent fully down; and that this was not a malfunction or cause for investigation for repair; especially since they functioned normally after the reset. The indication only looks for full up or full down deflection; so if they blew down a little due to reduction in trapped pressure; it made sense to them. Again they continued to function and indicated correctly the rest of the flight. Back to the VNAV function I used on the autopilot to meet the crossing restriction; as that is the recommended function to meet crossing restrictions; and the function I always use to reduce pilot workload. Somewhere during the sequence of the approximate 3;800-4;000FPM required descent the VNAV system apparently kicked off and defaulted back to just a raw pitch autopilot decent; in which with everything else going on I failed to notice. I can only attribute this to it not liking or taking issue with that rapid of a required decent; and thus defaulted out of it. With 1500+ hours in type; I cannot recall ever descending so rapidly; to were I would have seen or noticed its inability to function through that rapid of a decent. Had VNAV stayed activated; it would have saved the deviation from happening as the approach was loaded with all crossing restriction altitudes and it would have followed them; for which I was also expecting it to do. Although this 'event' happened in Tracon airspace; I feel the safety issue started back in Salt Lake Centers airspace by being left very high on the arrival. ATC needs to be cognizant especially when icing conditions are possible/present some or most aircraft cannot descend that rapidly and keep critical anti-ice/de-ice systems operating properly with idle power descent. Additionally; giving instruction to meet a crossing restriction that requires 3;500+FPM descents is unsafe and not conducive to being able to setup and properly execute a stabilized approach; and leads pilots to get behind. After giving this event thought I am recommending to our flight department to not use the VNAV function of the FMS/autopilot for required descents over 3;000 FPM; but rather use vertical speed mode and monitor carefully. In addition; we will no longer accept any crossing restrictions from ATC that would require over 3;000 FPM; and rather state unable and require a re-sequence back on the arrival via a course reversal to help lose altitude and keep from the pilot getting behind the aircraft and task saturated. Us pilot use the term 'slam dunk' when ATC tries to do this; where they keep you very high and then plop you right on the arrival/approach. This condition does present safety issues due to the above mentioned items.
Light Transport Single Pilot reported failing to cross arrival fix at assigned altitude resulting in a loss of ATC separation. Reporter also reported late descent clearance and inflight icing as contributing causes.