Inbound VFR PA31 and departing GLF4 have near midair collision overhead pdx.

Attributes
ACN	593978
Time
Date	200309
Day	Fri
Local Time Of Day	1201 To 1800
Place
Locale Reference	airport : pdx.airport
State Reference	OR
Altitude	msl single value : 2000
Environment
Flight Conditions	VMC
Light	Daylight
Aircraft 1
Controlling Facilities	tower : pdx.tower
Operator	common carrier : air taxi
Make Model Name	PA-31 Navajo Chieftan/Mojave/Navajo T1020
Operating Under FAR Part	Part 135
Flight Phase	descent : approach descent : intermediate altitude
Route In Use	approach : traffic pattern arrival : vfr
Flight Plan	VFR
Aircraft 2
Controlling Facilities	tower : pdx.tower
Operator	general aviation : corporate
Make Model Name	Gulfstream IV
Operating Under FAR Part	Part 121
Flight Phase	climbout : intermediate altitude
Person 1
Affiliation	company : air taxi
Function	flight crew : single pilot
Qualification	pilot : multi engine pilot : instrument pilot : cfi pilot : commercial
Experience	flight time last 90 days : 180 flight time total : 1400 flight time type : 150
ASRS Report	593978
Person 2
Affiliation	government : faa
Function	controller : local
Events
Anomaly	conflict : nmac
Independent Detector	other flight crewa
Resolutory Action	none taken : insufficient time
Consequence	faa : reviewed incident with flight crew
Miss Distance	horizontal : 0 vertical : 100
Supplementary
Problem Areas	Environmental Factor Flight Crew Human Performance Aircraft ATC Human Performance
Primary Problem	ATC Human Performance
Air Traffic Incident	Operational Error

Narrative:

I was instructed by pdx control tower to 'cross midfield at 2000 ft for left downwind runway 28L.' runway 28L&right are staggered by at least 3000 ft (runway 28L extends further west than runway 28R). As I crossed from north to south as instructed, midfield for left downwind runway 28L, a departing G4 on runway 28R crossed underneath me. I never saw the G4 until he was directly underneath my aircraft. The control tower was using only 1 of their 2 frequencys during peak arrival and departure times thus leaving the tower extremely busy. After the G4 passed below me, he reported the near miss to tower. I believe there were several contributing factors: 1) the staggered runways of 28L&right can create many 'midfield' crossing areas. What is considered midfield at pdx? 2) the rate of climb of the G4 and my airspeed were miscalculated by tower. 3) the tower never announced TA's to myself or the G4, not even after it was too late. My observation was that I crossed 'midfield' and complied with tower's instructions as stated. After the incident, on the ground talking with the control tower supervisor, he told myself and my assistant chief pilot that they (tower) never saw the conflict because they (tower) were looking the opposite direction.

Original NASA ASRS Text

Title: INBOUND VFR PA31 AND DEPARTING GLF4 HAVE NMAC OVERHEAD PDX.

Narrative: I WAS INSTRUCTED BY PDX CTL TWR TO 'CROSS MIDFIELD AT 2000 FT FOR L DOWNWIND RWY 28L.' RWY 28L&R ARE STAGGERED BY AT LEAST 3000 FT (RWY 28L EXTENDS FURTHER W THAN RWY 28R). AS I CROSSED FROM N TO S AS INSTRUCTED, MIDFIELD FOR L DOWNWIND RWY 28L, A DEPARTING G4 ON RWY 28R CROSSED UNDERNEATH ME. I NEVER SAW THE G4 UNTIL HE WAS DIRECTLY UNDERNEATH MY ACFT. THE CTL TWR WAS USING ONLY 1 OF THEIR 2 FREQS DURING PEAK ARR AND DEP TIMES THUS LEAVING THE TWR EXTREMELY BUSY. AFTER THE G4 PASSED BELOW ME, HE RPTED THE NEAR MISS TO TWR. I BELIEVE THERE WERE SEVERAL CONTRIBUTING FACTORS: 1) THE STAGGERED RWYS OF 28L&R CAN CREATE MANY 'MIDFIELD' XING AREAS. WHAT IS CONSIDERED MIDFIELD AT PDX? 2) THE RATE OF CLB OF THE G4 AND MY AIRSPD WERE MISCALCULATED BY TWR. 3) THE TWR NEVER ANNOUNCED TA'S TO MYSELF OR THE G4, NOT EVEN AFTER IT WAS TOO LATE. MY OBSERVATION WAS THAT I CROSSED 'MIDFIELD' AND COMPLIED WITH TWR'S INSTRUCTIONS AS STATED. AFTER THE INCIDENT, ON THE GND TALKING WITH THE CTL TWR SUPVR, HE TOLD MYSELF AND MY ASSISTANT CHIEF PLT THAT THEY (TWR) NEVER SAW THE CONFLICT BECAUSE THEY (TWR) WERE LOOKING THE OPPOSITE DIRECTION.

Data retrieved from NASA's ASRS site as of July 2007 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.