Narrative:

We had FMS meled due to database so we were operating using green needles. My first officer was recently out of training (60 hours). We had been given a heading to join the 117 radial to aml since esl was out of service and descend via starting at druzz. We intercepted what was indicating the 117 radial the HSI needle was jumpy. We crossed druzz at 15000 and continued descent to be at or above wewil at 14000. I was what I thought was passed wewil according to our indications and I had slowed descent to be at or above 12000 at nevyr. ATC asked us about our altitude and that we were low for wewil (we were at about 13500). They showed us 2 miles southwest of wewil. I replied that we showed passed wewil and immediately asked for vectors since at that point it was evident we were not getting correct indications on our nav. ATC gave us a heading and altitude and direct aml when able. We turned to that heading and went to the assigned altitude; which was lower than our current altitude which to me at least meant while we may have missed a crossing; at least there was no traffic below us. Upon descending to 11000 on the new heading; we then broke out of the clouds and at that point had iad and aml in sight and knew the new heading given by ATC was indeed getting us to aml. I verified with ATC that we were direct aml and they agreed that we were now heading the right direction. The rest of the STAR and descent went uneventful.the threats for this event were 1) no FMS in single FMS aircraft; leading us to rely on conventional nav; which is known to have errors. The sole source of navigation gave us no means of backup to verify until ATC advised us of the deviation. 2) having a low time first officer who was on his first flight ever into dca which can be overwhelming; and then adding no FMS on top of it which I believe was a first for him in the plane. While he was giving assistance as he could; being new; in a complex environment; with a nonstandard aircraft (mels)if in this situation again; I would definitely query ATC to verify that we are indeed where the indications say we are. We had briefed the arrival before descent and both felt we were ready for the arrival. I don't think if I was in this situation I would not accept the aircraft for this flight; but as I said earlier; I would definitely verify with ATC a lot more. Thought about loading flight plan in FMS using expired database; but decided against that because with an out of date database; getting possible inaccurate backup data could lead to far worse situation.it seems like at altitude when going to a station vs from or abeam a station; the green needles are never very strong. I don't know if this is due to the VOR antenna being on the tail; and when the station is off the nose; the signal having to pass through the cabin where there is a multitude of possible personal electronics; some which may not be in airplane mode. When we departed dca; we tracked from aml for 130 miles to the west and since the station was behind us; the needle was strong the entire way. Later in the flight we were given a 90 degree turn to bsv VOR; when bsv was off our side; it was strong; but once we were heading at it; it went back to its not as strong ways; if it is determined that passenger electronic interference is an issue; would this possibly be a situation where we may need to inconvenience passengers and at least while in terminal area; have all electronics off and not just airplane mode to account for passengers that may have something on and inadvertently not in airplane mode. This is an issue I have run into before when using conventional nav in the enroute and early terminal area; but luckily this is the first time where there has ever been a deviation due to it.

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Original NASA ASRS Text

Title: EMB-145 Captain reported being dispatched with the single FMS deferred inoperative and using VORs for navigation. The navigation became less reliable and the crew descended early on the arrival. PCT intervened and the crew received vectors and altitudes to the airport.

Narrative: We had FMS MELed due to database so we were operating using green needles. My FO was recently out of training (60 hours). We had been given a heading to join the 117 radial to AML since ESL was out of service and descend via starting at DRUZZ. We intercepted what was indicating the 117 radial the HSI needle was jumpy. We crossed DRUZZ at 15000 and continued descent to be at or above WEWIL at 14000. I was what I thought was passed WEWIL according to our indications and I had slowed descent to be at or above 12000 at NEVYR. ATC asked us about our altitude and that we were low for WEWIL (we were at about 13500). They showed us 2 miles SW of WEWIL. I replied that we showed passed WEWIL and immediately asked for vectors since at that point it was evident we were not getting correct indications on our nav. ATC gave us a heading and altitude and direct AML when able. We turned to that heading and went to the assigned altitude; which was lower than our current altitude which to me at least meant while we may have missed a crossing; at least there was no traffic below us. Upon descending to 11000 on the new heading; we then broke out of the clouds and at that point had IAD and AML in sight and knew the new heading given by ATC was indeed getting us to AML. I verified with ATC that we were direct AML and they agreed that we were now heading the right direction. The rest of the STAR and descent went uneventful.The threats for this event were 1) No FMS in single FMS aircraft; leading us to rely on conventional nav; which is known to have errors. The sole source of navigation gave us no means of backup to verify until ATC advised us of the deviation. 2) Having a low time FO who was on his first flight ever into DCA which can be overwhelming; and then adding no FMS on top of it which I believe was a first for him in the plane. While he was giving assistance as he could; being new; in a complex environment; with a nonstandard aircraft (MELs)If in this situation again; I would definitely query ATC to verify that we are indeed where the indications say we are. We had briefed the arrival before descent and both felt we were ready for the arrival. I don't think if I was in this situation I would not accept the aircraft for this flight; but as I said earlier; I would definitely verify with ATC a lot more. Thought about loading flight plan in FMS using expired database; but decided against that because with an out of date database; getting possible inaccurate backup data could lead to far worse situation.It seems like at altitude when going to a station vs from or abeam a station; the green needles are never very strong. I don't know if this is due to the VOR antenna being on the tail; and when the station is off the nose; the signal having to pass through the cabin where there is a multitude of possible personal electronics; some which may not be in airplane mode. When we departed DCA; we tracked FROM AML for 130 miles to the west and since the station was behind us; the needle was strong the entire way. Later in the flight we were given a 90 degree turn to BSV VOR; when BSV was off our side; it was strong; but once we were heading at it; it went back to its not as strong ways; If it is determined that passenger electronic interference is an issue; would this possibly be a situation where we may need to inconvenience passengers and at least while in terminal area; have all electronics off and not just airplane mode to account for passengers that may have something on and inadvertently not in airplane mode. This is an issue I have run into before when using conventional nav in the enroute and early terminal area; but luckily this is the first time where there has ever been a deviation due to it.

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.