EMB ERJ 145 ER/LR
Flight Crew Air Transport Pilot (ATP)
ATC Issue All Types; Aircraft Equipment Problem Less Severe; Deviation / Discrepancy - Procedural Published Material / Policy
Air Traffic Control Issued New Clearance; Flight Crew Requested ATC Assistance / Clarification
Aircraft
There was no violation that I know of; but I wanted to make the company aware of a problem in regard to RNAV arrivals and departures. We were on the KAROO one RNAV arrival into RDU with a northeast transition for Runway 5R. The routing information at the end of the arrival says to specifically fly a track of 232 after passing TOYER intersection. It doesn't say to fly a heading but to fly a specific outbound course to nowhere. The problem is that when we pass TOYER we received the caution message Lateral Mode Off and the airplane reverts to ROLL mode. Fortunately just before reaching that fix I asked for a heading as I have seen this very recently with any RNAV arrival or departure that specifies to fly a course after a particular fix rather than a heading. Specifically I saw this happen out of LGA also but again I had asked for a heading. Coming into RDU I wanted to test and see if the problem would happen again so I asked for a heading after TOYER and remained in LNAV mode until just passing the fix when we received the caution message and roll mode. Let me explain exactly how I had the arrival and approach setup in the FMS. On the arrival page we had selected: RW05R ILS HPW.KAROO1 On the flight plan page it looked like this after the STINT intersection on the arrival: 233 degrees to TOYER after TOYER it says to fly 232 degrees or as assigned followed by a discontinuity message prior to starting actual approach. Like I said I asked for a heading from ATC to head off the problem which he gave me a heading of 230 degrees. After a minute or two though the Controller then asked why we had asked for a heading if we were supposed to be on the RNAV arrival. I just let him know that we were on the RNAV arrival and that we had a conflict and requested a heading. Please look into this as either I am doing something wrong or our aircraft are unable to fly RNAV arrivals and departures that end with flying a course to nowhere instead of a heading. Fortunately there was no pilot deviation that I know of; but I am trying to stop a problem before it does cause a deviation.
EMB145 Captain believes his aircraft is not correctly flying a 'track' after the last fix on an RNAV arrival. In this case the KAROO 1 RNAV arrival to RDU.