Narrative:

I was descending through approximately 16;000 feet on an RNAV arrival. ATC instructed me to 'descend via the arrival.' the published bottom altitude was 6;000 feet; and as such; I set the MCP altitude to 6;000 feet while descending in the VNAV mode with all speed and crossing altitude restrictions verified in the FMC prior to descent. At approximately 16;000 feet the ATC controller said we could delete the speed restrictions on the remainder of the arrival. When I looked at the legs page of the FMC I observed there were five more altitude crossing restrictions remaining on the arrival; the first restriction to cross between 13;000-10;000 feet; the second at 10;000 feet; the third at 9;000 feet; the fourth at/or below 8;000 feet; and the fifth (bottom altitude) at 6;000 feet. The first crossing restriction between 13;000-10;000 feet also had a published speed of 250 KTS. Because the ATC controller said we could delete the speed restrictions; I referenced the FMC legs page to delete the speed restrictions. However; I realized that the FMC would not allow me to delete only the speed restrictions without also deleting the altitude restrictions. The first; most expeditious; and practical way of flying the rest of the arrival without the speed restrictions; I thought; was to use the 'vertical speed' mode of the AFDS. This way I could have the speed window open/available to control the speed and control the vertical descent with 'vertical speed.' this worked well for the first crossing restriction; between 13;000-10;000 feet. The problem occurred with the second crossing restriction at 10;000 feet. Because the MCP altitude window was set at 6;000 feet; and the aircraft was descending in 'vertical speed' mode; not in VNAV mode; the aircraft descended to approximately 9;650 feet 3-5 NM prior to the crossing restriction. As soon as I realized this; I immediately selected 'altitude hold' on the MCP. Once the aircraft leveled off; I reset the MCP altitude window to 10;000 feet and using the 'vertical speed' recaptured the altitude of 10;000 feet. After this point we were back on the profile and I selected VNAV for the remainder of the descent. The ATC controller never called us to advise us of any deviation. Shortly after passing the next crossing altitude of 9;000 feet; he advised us to delete the following crossing altitude restriction of 8;000 feet and continue descending on the arrival (bottom altitude 6;000 feet). With RNAV sids and stars being more prevalent; these types of scenarios and a review of these procedures should be focused on more during recurrent training. Discussing the problems that can be encountered when flying these procedures; particularly when ATC makes amendments to the published arrivals (speeds/altitudes); would be helpful. Also; a good idea would be to offer pilots some useful techniques to use when amendments to the published procedures are issued by ATC.

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Original NASA ASRS Text

Title: B737 Captain on the IVANE5 Arrival to CLT descending through 16;000 feet is cleared to descend via the IVANE5 and delete the speed restrictions. This cannot be easily accomplished in the FMC; so manual control of the MCP is initiated and results in an overshoot of a 10;000 foot restriction.

Narrative: I was descending through approximately 16;000 feet on an RNAV arrival. ATC instructed me to 'descend via the arrival.' The published bottom altitude was 6;000 feet; and as such; I set the MCP altitude to 6;000 feet while descending in the VNAV mode with all speed and crossing altitude restrictions verified in the FMC prior to descent. At approximately 16;000 feet the ATC controller said we could delete the speed restrictions on the remainder of the arrival. When I looked at the LEGS page of the FMC I observed there were five more altitude crossing restrictions remaining on the arrival; the first restriction to cross between 13;000-10;000 feet; the second at 10;000 feet; the third at 9;000 feet; the fourth at/or below 8;000 feet; and the fifth (bottom altitude) at 6;000 feet. The first crossing restriction between 13;000-10;000 feet also had a published speed of 250 KTS. Because the ATC controller said we could delete the speed restrictions; I referenced the FMC legs page to delete the speed restrictions. However; I realized that the FMC would not allow me to delete only the speed restrictions without also deleting the altitude restrictions. The first; most expeditious; and practical way of flying the rest of the arrival without the speed restrictions; I thought; was to use the 'Vertical Speed' mode of the AFDS. This way I could have the speed window open/available to control the speed and control the vertical descent with 'Vertical Speed.' This worked well for the first crossing restriction; between 13;000-10;000 feet. The problem occurred with the second crossing restriction at 10;000 feet. Because the MCP altitude window was set at 6;000 feet; and the aircraft was descending in 'Vertical Speed' mode; not in VNAV mode; the aircraft descended to approximately 9;650 feet 3-5 NM prior to the crossing restriction. As soon as I realized this; I immediately selected 'Altitude Hold' on the MCP. Once the aircraft leveled off; I reset the MCP altitude window to 10;000 feet and using the 'Vertical Speed' recaptured the altitude of 10;000 feet. After this point we were back on the profile and I selected VNAV for the remainder of the descent. The ATC controller never called us to advise us of any deviation. Shortly after passing the next crossing altitude of 9;000 feet; he advised us to delete the following crossing altitude restriction of 8;000 feet and continue descending on the arrival (bottom altitude 6;000 feet). With RNAV SIDs and STARs being more prevalent; these types of scenarios and a review of these procedures should be focused on more during recurrent training. Discussing the problems that can be encountered when flying these procedures; particularly when ATC makes amendments to the published arrivals (speeds/altitudes); would be helpful. Also; a good idea would be to offer pilots some useful techniques to use when amendments to the published procedures are issued by ATC.

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.