B737 flight crew experience a VNAV disconnect during the HYDRR1 RNAV arrival into phx approaching ch...

Attributes
ACN	1276865
Time
Date	201507
Local Time Of Day	1201-1800
Place
Locale Reference	PHX.Airport
State Reference	AZ
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Make Model Name	B737 Undifferentiated or Other Model
Operating Under FAR Part	Part 121
Flight Phase	Descent Initial Approach
Route In Use	STAR HYDRR1 Arrival
Flight Plan	IFR
Component
Aircraft Component	Autoflight System
Person 1
Function	Pilot Flying First Officer
Qualification	Flight Crew Air Transport Pilot (ATP)
Experience	Flight Crew Last 90 Days 218
Person 2
Function	Captain Pilot Not Flying
Qualification	Flight Crew Air Transport Pilot (ATP)
Experience	Flight Crew Last 90 Days 189 Flight Crew Type 10769
Events
Anomaly	Deviation - Altitude Crossing Restriction Not Met Deviation - Altitude Overshoot Deviation - Procedural Clearance Deviation - Procedural Published Material / Policy Deviation - Speed All Types Inflight Event / Encounter Weather / Turbulence

Narrative:

While conducting the HYDRR1 RNAV arrival into phx in a B737; we were directed by ATC to keep our speed at 300 knots until geela; and then comply with speeds at geela. We complied with this; and as we approached geela we were given a speed reduction; which we complied with. At .3 DME prior to chavo with the aircraft in LNAV/VNAV path; the aircraft was leveling at 9000 feet at 210 knots as depicted on the arrival. It was mid-afternoon in phx with temperature in the low 100s and occasional moderate turbulence. At this point I received a VNAV disconnect message; which I cleared. In the few seconds it took to assess what the aircraft was doing; and reengage a mode on the MCP; the aircraft may have crossed chavo up to 200 feet low since I had the bottom altitude of 7000 feet in the altitude window while the airplane was VNAV path. I had applied a little power while determining whether I needed to level or continue descent. Now; (maybe five seconds after the disconnect) we were past chavo. I decided to idle the power; dial 1000 FPM into vertical speed and continue the descent to comply with lemoe at 7000 feet. With the turbulence and the disconnect; the speed had accelerated to near 230 knots. I deployed speed boards to slow the aircraft back to 210 knots while continuing to comply with the lemoe crossing restriction.

Original NASA ASRS Text

Title: B737 flight crew experience a VNAV disconnect during the HYDRR1 RNAV Arrival into PHX approaching CHAVO. CHAVO may have been crossed 200 feet low and the speed was allowed to increase above the CHAVO limit of 210 knots.

Narrative: While conducting the HYDRR1 RNAV Arrival into PHX in a B737; we were directed by ATC to keep our speed at 300 knots until GEELA; and then comply with speeds at GEELA. We complied with this; and as we approached GEELA we were given a speed reduction; which we complied with. At .3 DME prior to CHAVO with the aircraft in LNAV/VNAV PATH; the aircraft was leveling at 9000 feet at 210 knots as depicted on the arrival. It was mid-afternoon in PHX with temperature in the low 100s and occasional moderate turbulence. At this point I received a VNAV disconnect message; which I cleared. In the few seconds it took to assess what the aircraft was doing; and reengage a mode on the MCP; the aircraft may have crossed CHAVO up to 200 feet low since I had the bottom altitude of 7000 feet in the Altitude window while the airplane was VNAV PATH. I had applied a little power while determining whether I needed to level or continue descent. Now; (maybe five seconds after the disconnect) we were past CHAVO. I decided to idle the power; dial 1000 FPM into Vertical Speed and continue the descent to comply with LEMOE at 7000 feet. With the turbulence and the disconnect; the speed had accelerated to near 230 knots. I deployed speed boards to slow the aircraft back to 210 knots while continuing to comply with the LEMOE crossing restriction.

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.

B737 flight crew experience a VNAV disconnect during the HYDRR1 RNAV arrival into phx approaching chavo. Chavo may have been crossed 200 feet low and the speed was allowed to increase above the chavo limit of 210 knots.