A fractional jet crew began an early descent on the bos runway 4R localizer outside of nabbo because...

Narrative:

We were on approach and cleared for the localizer 4R approach; to maintain 3000 'til established; 170 KTS to millt. The FMS was set up for the approach from millt. The approach called for us to be at 3000 to nabbo and then descend to 1800' from nabbo to millt. Once we were cleared for the approach; I checked the FMS to see where we were in relation to nabbo. Nabbo wasn't in the FMS; so I put it in. It immediately went to the top and turned orange which indicated to me that we were inside of nabbo and could commence the descent to be at 1800' by millt. Shortly after the captain commenced the descent; I thought something was wrong. I checked the DME distance and realized that we were in fact still outside of nabbo. At that same instant ATC called and said that we were still outside nabbo and that we were to level off at 2000 or go back to 3000. Captain arrested the descent and began a climb back to 3000. At this time I was trying to determine what had caused the error on the FMS and didn't notice the captain was also watching me; hence we didn't notice the speed was decaying. Once again ATC informed us to maintain 170 KTS at the same time we notice the speed was falling back (it was at about 120 KTS at this point). Captain once again re-established the correct speed and altitude and we continued on the approach and landed without any further incident.a major contributor to this event was the automation. Also we (I) should have checked the DME sooner and not relied so much on the FMS. Also if we had of had the scale on the mfd at larger setting we may have picked up the error a lot sooner and have been more situationally aware.

Original NASA ASRS Text

Title: A fractional jet crew began an early descent on the BOS Runway 4R LOC outside of NABBO because the FMS did not properly display NABBO and additionally the DME was not verified. While correcting for the ATC discovered altitude deviation; the aircraft speed deviated below ATC requested speed.

Narrative: We were on Approach and cleared for the LOC 4R approach; to maintain 3000 'til established; 170 KTS to MILLT. The FMS was set up for the approach from MILLT. The approach called for us to be at 3000 to NABBO and then descend to 1800' from NABBO to MILLT. Once we were cleared for the approach; I checked the FMS to see where we were in relation to NABBO. NABBO wasn't in the FMS; so I put it in. It immediately went to the top and turned orange which indicated to me that we were inside of NABBO and could commence the descent to be at 1800' by MILLT. Shortly after the Captain commenced the descent; I thought something was wrong. I checked the DME distance and realized that we were in fact still outside of NABBO. At that same instant ATC called and said that we were still outside NABBO and that we were to level off at 2000 or go back to 3000. Captain arrested the descent and began a climb back to 3000. At this time I was trying to determine what had caused the error on the FMS and didn't notice the Captain was also watching me; hence we didn't notice the speed was decaying. Once again ATC informed us to maintain 170 KTS at the same time we notice the speed was falling back (it was at about 120 KTS at this point). Captain once again re-established the correct speed and altitude and we continued on the approach and landed without any further incident.A major contributor to this event was the automation. Also we (I) should have checked the DME sooner and not relied so much on the FMS. Also if we had of had the scale on the MFD at larger setting we may have picked up the error a lot sooner and have been more situationally aware.

Data retrieved from NASA's ASRS site as of April 2012 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.

Attributes
ACN	840606
Time
Date	200906
Local Time Of Day	1201-1800
Place
Locale Reference	BOS.Airport
State Reference	MA
Environment
Flight Conditions	IMC
Light	Night
Aircraft 1
Make Model Name	Light Transport Low Wing 2 Turbojet Eng
Operating Under FAR Part	Part 91
Flight Phase	Initial Approach
Flight Plan	IFR
Component
Aircraft Component	FMS/FMC
Person 1
Function	First Officer Pilot Not Flying
Qualification	Flight Crew Air Transport Pilot (ATP)
Events
Anomaly	Aircraft Equipment Problem Less Severe Deviation - Altitude Excursion From Assigned Altitude Deviation - Procedural Clearance Deviation - Procedural Published Material / Policy Deviation - Speed All Types

A fractional jet crew began an early descent on the bos runway 4R localizer outside of nabbo because the FMS did not properly display nabbo and additionally the DME was not verified. While correcting for the ATC discovered altitude deviation; the aircraft speed deviated below ATC requested speed.