Date: 201408
Local time of day: 1801-2400
Location: ZME.ARTCC, TN
Flight conditions: VMC
Weather elements / visibility: 10
Light: Daylight
Aircraft: Learjet 35
Operator: Air Taxi
Operating under: Part 91
Flight plan: IFR
Mission: Cargo / Freight / Delivery
Flight phase: Descent
Airspace: Class E ZME
ATC / advisory: Center ZME
Reporter organization: Air Taxi
Reporter function: Pilot Not Flying; Captain
Reporter qualification: Flight Crew Instrument; Flight Crew Flight Instructor; Flight Crew Air Transport Pilot (ATP); Flight Crew Multiengine; Flight Crew Flight Engineer
Human factors: Workload; Distraction
Anomaly: Deviation - Altitude Crossing Restriction Not Met; Deviation / Discrepancy - Procedural Clearance; Deviation / Discrepancy - Procedural Published Material / Policy
Detector: Person Flight Crew
When detected: In-flight
Result: Air Traffic Control Issued New Clearance; Flight Crew Requested ATC Assistance / Clarification
Contributing factors: Human Factors; Chart Or Publication
Primary problem: Human Factors

Narrative: First Officer flying. I was off frequency to get ATIS. While I was off; ATC gave us 'descend via the WLDER 8.' I came back on frequency. First Officer informed me of the clearance. He descended to cross SPKER intersection at FL230 and 280 knots. He made that restriction just fine. (Chart says to cross SPKER at FL230 or below and 280 KIAS.) However; the next restriction is at LTOWN intersection at 10;000 feet and 230 KIAS (we were landing south). The problem is that if you cross SPKER exactly at FL230 and 280 KIAS; it is physically impossible to make the LTOWN restriction. SPKER to LTOWN is only 19 nautical miles. I realize the SPKER restriction is FL230 or below; but this is misleading. In my mind; no STAR should be designed to be impossible to satisfy--making one restriction; impossible to make the next. The STAR should be changed. Delete the FL230 (keep the 280 KIAS) at SPKER. We design STAR's to not only satisfy ATC airspace requirements; but also to provide fuel-efficient; safe; and quiet descents. This philosophy was first initiated in the 'profile descents' at Denver in the late 70's and early 80's. A 'normal' profile to meet the LTOWN restriction would be to cross SPKER at about 15;000 feet (3:1 descent profile plus allowance to slow from 280 KIAS to 230 KIAS). This is quite a difference from the at-or-below FL230 published at SPKER. Even if Memphis is landing north; FL230 to 16;000 feet (SPKER/LTOWN) is 7;000 feet to lose. A 3:1 profile would require 21 nautical miles; with only 19 nautical miles between the two fixes. Again; I understand the restriction at SPKER is FL230 or below. But; again; the published altitude and speed restrictions should allow for a reasonable descent profile.

Callback: The reporter states that his aircraft is not equipped with an FMC or autothrust and requires a great deal of planning to comply with OPD's with altitude windows that vary with the landing direction. The LR35 can descend very rapidly with full spoilers so the thinking was that if the SPKER restriction was made; the next one at LTOWN could be made. Not true even in the LR35. Suggest removing the altitude restriction at SPKER entirely or making it much lower.



Synopsis: Captain of a non FMC LR35 reports missing the crossing restriction at LTOWN; while on the WLDER8 STAR; landing south with the First Officer flying; after making the restriction at SPKER; due to an excessive amount of altitude to lose by LTOWN.