Date: 201404
Local time of day: 1201-1800
Location: MDW.Airport, IL
Flight conditions: VMC
Light: Daylight
Aircraft: B737-700
Operator: Air Carrier
Operating under: Part 121
Flight plan: IFR
Mission: Passenger
Flight phase: Descent
Airspace: Class E C90
ATC / advisory: TRACON C90
Aircraft component: FMS/FMC
Component problem: Design; Improperly Operated
Reporter organization: Air Carrier
Reporter function: First Officer; Pilot Flying
Human factors: Human-Machine Interface; Situational Awareness
Second reporter function: Captain; Pilot Not Flying
Anomaly: ATC Issue All Types; Deviation - Track / Heading All Types; Deviation / Discrepancy - Procedural Published Material / Policy; Deviation / Discrepancy - Procedural Clearance
Detector: Person Air Traffic Control
Result: Air Traffic Control Issued Advisory / Alert; Air Traffic Control Issued New Clearance; Flight Crew Became Reoriented
Contributing factors: Aircraft; Human Factors; Procedure
Primary problem: Ambiguous

Narrative: We were on the ENDEE 1 Arrival into MDW. The arrival had been properly briefed. The first ATIS we received showed an ILS for [Runway] 31C. We were approaching POOGY and given a crossing restriction of FL240. Next; we received crossing restriction of NANEE at 17;000 FT. Shortly thereafter; we were given 'descend via the ENDEE One Arrival.' With the previously two changes from the published arrival; we were almost 4;000 FT high on the profile. I increased the speed to over 300 KTS and caught back up to the path before MMEGG. A new ATIS came out and was advertising [Runway] 31C circle [Runway] 22L. We revised the runway in the box to [Runway] 22L with GLEAM and RUNTS added in. After passing STKNY; ATC queried our headed. We then realized that when [Runway] 22L was changed in the box the arrival fix sequencing changed too. We were then given a heading 090 and told 'no worries.'I should have noticed the change and rebriefed the approach. Although we should have software available to allow a different landing runway with the ability to fly a different transition; if not; you could potentially be close to the field with a lot of programming required. MDW had previously been utilizing the RNAV Y and Z approaches for [Runway] 22L. Also; due to the changes to the crossing restrictions on the arrival; my full attention was on trying to get back on the path. If we were allowed to 'descend via' the entire arrival I could have caught the error in fix sequencing.


Second narrative: We were flying the ENDEE 1 Arrival into MDW starting at POOGY. The ATIS for MDW called for landing on 31C. The arrival was briefed by the First Officer who was flying and all points and altitudes on the arrival were confirmed by me; the pilot monitoring. At the start of the arrival; Chicago Center changed the crossing restriction at NANEE to 170 versus the charted 150B. In the descent; we were switched to Chicago Approach and checked in with the ATIS. As we were approaching NANEE and leveling a 170; they told us the ATIS had changed and to descend via the ENDEE 1 with the 31C transition. This put us high on our descent profile so we had to change the aircraft speed to make the crossing restriction. While the First Officer was doing this; I got the new ATIS which now called for an ILS to 31C circling to 22L. We then turned our attention to crossing MMEGG 100B; which took some speed changes and speedbrake application but we made it. After passing MMEGG; the First Officer programmed the FMC for the new landing Runway 22L. He kept the 31C ILS points to HOBEL and then inserted 22L with a 2.5 NM extension; which equated to about where the smokestacks are located on the 22L final. I verified and concurred with the changes. Finally; it appeared we had everything ready for the arrival in MDW. Shortly after passing STKNY; Chicago asked us what our heading was. When I replied 061; they said; 'You appear to be flying the 22L transition. Turn right to 090 for radar vectors.' We then flew the ILS 31C circle to 22L without further incident.This is the second ASAP I have filed for the ENDEE Arrival; both were because Chicago Center changed an altitude on the arrival to a hard altitude above; at; or below altitude. This caused us to be high when cleared to descend via and ultimately leading to the errors. These arrivals are designed to be flown at the published altitudes and Chicago Center changes them every time. Plan on getting more reports from this arrival. I think the circle to land option is unique to MDW; but we found that if you input the landing runway; not even with an approach associated; it would change the arrival transition. Since we had already briefed and verified the arrival and transition; we thought the ATIS change and subsequent runway change didn't affect our programming. I think it needs to be emphasized that the transitions are based on the runway transition ATC wants you to fly and may [are] not be the actual landing runway.


Synopsis: Air carrier flight crew learns that the ENDEE 1 transitions into MDW are determined by the runway selection in the FMC. A clearance to fly the Runway 31C transition and circle to land Runway 22L results in a track deviation when Runway 22L is entered prior to passing STKNY.