A B737-300 flight crew failed to make a descent crossing restriction and the first officer cited the...

Attributes
ACN	817049
Time
Date	200812
Local Time Of Day	1201 To 1800
Place
Locale Reference	airport : fll.airport
State Reference	FL
Altitude	msl single value : 24000
Environment
Flight Conditions	VMC
Aircraft 1
Controlling Facilities	artcc : zma.artcc tower : zzz.tower
Operator	common carrier : air carrier
Make Model Name	B737-300
Operating Under FAR Part	Part 121
Navigation In Use	other
Flight Phase	descent : intermediate altitude
Route In Use	arrival star : n/s
Flight Plan	IFR
Person 1
Affiliation	company : air carrier
Function	flight crew : first officer
Qualification	pilot : atp
Experience	flight time last 90 days : 100 flight time total : 9000 flight time type : 300
ASRS Report	817049
Events
Anomaly	aircraft equipment problem : less severe altitude deviation : crossing restriction not met non adherence : clearance
Independent Detector	other flight crewa
Resolutory Action	none taken : detected after the fact
Supplementary
Problem Areas	Aircraft Flight Crew Human Performance
Primary Problem	Flight Crew Human Performance

Narrative:

On STAR to fll; cleared to cross fathr intersection at FL240. The VNAV in this series of aircraft just plain doesn't work. It will almost always miss all crossing restrictions by 3-5 miles; unless you have a strong headwind. Consequently; from experience (and from observing the other pilots I fly with; all of whom have considerably more experience on the aircraft than I do); I have learned to descend manually; in vertical speed or level change mode. In this instance; I started to descend in vertical speed with the intention of switching to level change later. I then got distracted or interrupted and forgot to switch descent modes until it was too late; and missed the crossing restriction. Factor #1: economics. Airlines have determined that it is cheapest to descend at idle; and fmss are programmed to descend so as to arrive exactly at the bottom of descent point at idle; and then add power at or after that point. Heaven forbid that we arrive and add power a mile (i.e. 10-15 seconds) early. Factor #2: the crappy fmss in the B737-300s don't work and always miss crossing restrictions. Factor #3: I got distracted and didn't remember to do all of the jobs that the FMS should be able to do in the first place.

Original NASA ASRS Text

Title: A B737-300 flight crew failed to make a descent crossing restriction and the First Officer cited the consistently poor vertical navigation performance of the FMS.

Narrative: On STAR to FLL; cleared to cross FATHR intersection at FL240. The VNAV in this series of aircraft just plain doesn't work. It will almost always miss all crossing restrictions by 3-5 miles; unless you have a strong headwind. Consequently; from experience (and from observing the other pilots I fly with; all of whom have considerably more experience on the aircraft than I do); I have learned to descend manually; in vertical speed or level change mode. In this instance; I started to descend in vertical speed with the intention of switching to level change later. I then got distracted or interrupted and forgot to switch descent modes until it was too late; and missed the crossing restriction. Factor #1: Economics. Airlines have determined that it is cheapest to descend at idle; and FMSs are programmed to descend so as to arrive exactly at the bottom of descent point at idle; and then add power at or after that point. Heaven forbid that we arrive and add power a mile (i.e. 10-15 seconds) early. Factor #2: The crappy FMSs in the B737-300s don't work and always miss crossing restrictions. Factor #3: I got distracted and didn't remember to do all of the jobs that the FMS should be able to do in the first place.

Data retrieved from NASA's ASRS site as of May 2009 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.

A B737-300 flight crew failed to make a descent crossing restriction and the first officer cited the consistently poor vertical navigation performance of the FMS.