Narrative:

While preflighting emb-505; a phenom 300; we discovered that the emergency brake accumulator pressure had bled down overnight and was showing zero (0). Normally this system indicates 2700-3000 psi (green range on the digital synoptic); and I have never seen it below that unless we intentionally bled the system down to zero (0). Some background information on this: we are required to bleed the system every 15-days to check the hydraulic system; and this is an approved procedure in our aom. When we do this; we disable both the normal and emergency brake systems; including the parking brake. Until an engine is started to restore pressure to the system we have no braking ability. Once the engine restores emergency brake accumulator pressure; the system holds the normal 2700-3000 range until it is intentionally bled down again.when I discovered the emergency brake pressure was zero I called maintenance. They told me that 'they are known to do that from time to time' and that this was not a maintenance squawk. I told him that I had never heard of this and that I was under the impression the pressure had to be in the green. He challenged me to find something in our checklist that says that; so we agreed that I would call him back after I looked. I couldn't find any reference for the system at all in any aom procedure; the poh; or the afm. To my knowledge; there is no mention of it having to hold pressure or not in any of these documents; nor is there a flight operations bulletin; aob; manufacturer's guidance letters; or any other guidance on this one way or another. However there is guidance in the MEL. The low pressure triggers an amber crew alerting system (cas) caution message; and the MEL indicates a 'no dispatch' condition if this cas message is present. There is wording to allow for crew actions that create this message to be excluded from the no dispatch condition (the 15-day check; for example); but in this case that was not relevant. I had flown the plane the night prior; and the security seal that I placed on the airplane was still there when we arrived yesterday morning.I called the maintenance controller back and informed him that the MEL indicated this was a grounding item; and that since there was no documentation that indicated that a pressure bleed-down was normal as he had suggested; that I would be sending in an aircraft on ground (aog) squawk. At this point he told me that before I did that the assistant chief pilot (acp) wanted to speak to me. The acp said that the MEL only applied if the engines were running; that this was not a squawk; and that if I continued to disagree that this would be escalated to our chief pilot (cp). I told the acp that I wasn't comfortable and to go ahead and escalate the issue. At that point they got off the phone and said they would call back once they got in touch with the cp. The acp and maintenance controller called me back and said that this had been escalated to director of operations (do) (who was not on the phone and there was no mention of whether or not cp had been informed) and that the director of operations had told me to go out and start an engine; check to see if the system held pressure with the engine running and if it quickly bled down after shutdown. I informed them both that I was not able to perform a maintenance procedure for them; but that I would be happy to perform the 15-day hydraulic check (which is almost identical to this) since that is an approved procedure in our aom for crews to do. I also stated that my intention was to ground the airplane regardless of the outcome of the test; since a successful test didn't erase the fact that somehow the system lost pressure overnight. They did not agree with this but said that if it passed the test to call them back and we would go from there. After hanging up I began to make arrangements with the FBO to perform the test and my phone rang again. It was the acp and maintenance controller telling me to disregard the test; that it wasn't necessary if I was going write it up anyway. They said just send it in; and that's how the event concluded.here are my concerns/questions:-I was told by the maintenance controller that this happens often and that it's normal. However; the MEL indicates that this should be a grounding item. As best I can tell; the assertion that this is not a squawk is in direct conflict with the MEL.-in almost a year of flying the phenom; I have never seen this. I have never even heard of it. I've picked up planes that had been sitting for several days and the emergency brake pressure was still well within the green range of 2700-3000 psi. I asked the maintenance controller and acp if this was a common occurrence; what was the root cause of it. They didn't know. If they don't know the underlying cause; how can they be sure that it isn't a squawk? How do they know this is 'normal?' -if this is really something that's happening frequently there should be written guidance that allows the plane to be flown when this happens (if they are correct that this isn't an abnormal condition); the MEL should be changed; or they should stop pressuring crews to fly it. At one point the acp asked the controller what the tolerance was for pressure bleed-down and the controller said that there is no guidance at all; even in the maintenance manual (M/M). There is nothing to indicate that it should; or should not; hold pressure over an extended period of time; or how much pressure loss is acceptable.-I received significant pressure to fly the airplane after I brought the MEL guidance to their attention. The maintenance controller was polite and professional; but the acp began pushing the instant he got on the phone. He told me 'this isn't a squawk' repeatedly; said that the MEL doesn't apply unless the engines are running (there is nothing I could find in the MEL that supports that statement); and suggested that the previous crew had done a 15-day check the night prior without any idea if that were true (it wasn't; I had flown the plane the night prior and had not done any check of the system).I'm concerned that there could be a serious safety issue lurking here. Nobody seems to know what's causing this issue; or if it could result in a total brake failure. At the very least; clear guidance should be provided so that crews aren't operating an airplane that the MEL indicates is not airworthy. Airline transport pilot.

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Original NASA ASRS Text

Title: Captain describes his efforts to explain to a Maintenance Controller and the Assistant Chief Pilot why their EMB-505 (Phenom 300) aircraft was not airworthy after he discovered the Emergency Brake accumulator had bled down to zero overnight. ACP continued to pressure pilot to accept aircraft as is; even after being informed the MEL language indicates a 'No Dispatch condition'. Pilot refused. Aircraft does not have Thrust Reversers.

Narrative: While preflighting EMB-505; a Phenom 300; we discovered that the Emergency Brake accumulator pressure had bled down overnight and was showing zero (0). Normally this system indicates 2700-3000 psi (green range on the digital synoptic); and I have never seen it below that unless we intentionally bled the system down to zero (0). Some background information on this: We are required to bleed the system every 15-days to check the hydraulic system; and this is an approved procedure in our AOM. When we do this; we disable both the Normal and Emergency Brake systems; including the Parking brake. Until an engine is started to restore pressure to the system we have no braking ability. Once the engine restores Emergency Brake accumulator pressure; the system holds the normal 2700-3000 range until it is intentionally bled down again.When I discovered the Emergency Brake pressure was zero I called Maintenance. They told me that 'they are known to do that from time to time' and that this was not a maintenance squawk. I told him that I had never heard of this and that I was under the impression the pressure had to be in the green. He challenged me to find something in our checklist that says that; so we agreed that I would call him back after I looked. I couldn't find any reference for the system at all in any AOM procedure; the POH; or the AFM. To my knowledge; there is no mention of it having to hold pressure or not in any of these documents; nor is there a Flight Operations Bulletin; AOB; Manufacturer's Guidance Letters; or any other guidance on this one way or another. However there is guidance in the MEL. The low pressure triggers an amber Crew Alerting System (CAS) Caution message; and the MEL indicates a 'NO DISPATCH' condition if this CAS message is present. There is wording to allow for crew actions that create this message to be excluded from the NO DISPATCH condition (the 15-Day Check; for example); but in this case that was not relevant. I had flown the plane the night prior; and the security seal that I placed on the airplane was still there when we arrived yesterday morning.I called the Maintenance Controller back and informed him that the MEL indicated this was a Grounding item; and that since there was no documentation that indicated that a pressure bleed-down was normal as he had suggested; that I would be sending in an Aircraft On Ground (AOG) squawk. At this point he told me that before I did that the Assistant Chief Pilot (ACP) wanted to speak to me. The ACP said that the MEL only applied if the engines were running; that this was not a squawk; and that if I continued to disagree that this would be escalated to our Chief Pilot (CP). I told the ACP that I wasn't comfortable and to go ahead and escalate the issue. At that point they got off the phone and said they would call back once they got in touch with the CP. The ACP and Maintenance Controller called me back and said that this had been escalated to Director of Operations (DO) (who was not on the phone and there was no mention of whether or not CP had been informed) and that the Director of Operations had told me to go out and start an engine; check to see if the system held pressure with the engine running and if it quickly bled down after shutdown. I informed them both that I was not able to perform a maintenance procedure for them; but that I would be happy to perform the 15-day hydraulic check (which is almost identical to this) since that is an approved procedure in our AOM for crews to do. I also stated that my intention was to ground the airplane regardless of the outcome of the test; since a successful test didn't erase the fact that somehow the system lost pressure overnight. They did not agree with this but said that if it passed the test to call them back and we would go from there. After hanging up I began to make arrangements with the FBO to perform the test and my phone rang again. It was the ACP and maintenance Controller telling me to disregard the test; that it wasn't necessary if I was going write it up anyway. They said just send it in; and that's how the event concluded.Here are my concerns/questions:-I was told by the Maintenance Controller that this happens often and that it's normal. However; the MEL indicates that this should be a Grounding item. As best I can tell; the assertion that this is not a squawk is in direct conflict with the MEL.-In almost a year of flying the Phenom; I have never seen this. I have never even heard of it. I've picked up planes that had been sitting for several days and the emergency brake pressure was still well within the green range of 2700-3000 PSI. I asked the Maintenance Controller and ACP if this was a common occurrence; what was the root cause of it. They didn't know. If they don't know the underlying cause; how can they be sure that it isn't a squawk? How do they know this is 'normal?' -If this is really something that's happening frequently there should be written guidance that allows the plane to be flown when this happens (if they are correct that this isn't an abnormal condition); the MEL should be changed; or they should stop pressuring crews to fly it. At one point the ACP asked the Controller what the tolerance was for pressure bleed-down and the Controller said that there is no guidance at all; even in the Maintenance Manual (M/M). There is nothing to indicate that it should; or should not; hold pressure over an extended period of time; or how much pressure loss is acceptable.-I received significant pressure to fly the airplane after I brought the MEL guidance to their attention. The Maintenance Controller was polite and professional; but the ACP began pushing the instant he got on the phone. He told me 'this isn't a squawk' repeatedly; said that the MEL doesn't apply unless the engines are running (there is nothing I could find in the MEL that supports that statement); and suggested that the previous crew had done a 15-Day Check the night prior without any idea if that were true (it wasn't; I had flown the plane the night prior and had not done any check of the system).I'm concerned that there could be a serious safety issue lurking here. Nobody seems to know what's causing this issue; or if it could result in a total brake failure. At the very least; clear guidance should be provided so that crews aren't operating an airplane that the MEL indicates is not airworthy. Airline Transport Pilot.

Data retrieved from NASA's ASRS site and automatically converted to unabbreviated mixed upper/lowercase text. This report is for informational purposes with no guarantee of accuracy. See NASA's ASRS site for official report.