Date: 201308
Local time of day: 1201-1800
Location: BFI.Airport, WA
Flight conditions: VMC
Weather elements / visibility: Clear; 10
Light: Daylight
Aircraft: M-20 K (231) / Encore
Operator: Personal
Operating under: Part 91
Flight plan: None
Mission: Personal
Flight phase: Takeoff / Launch
Airspace: Class D BFI
ATC / advisory: Tower BFI
Reporter organization: Personal
Reporter function: Pilot Flying; Single Pilot
Reporter qualification: Flight Crew Air Transport Pilot (ATP); Flight Crew Multiengine; Flight Crew Instrument; Flight Crew Flight Engineer
Human factors: Situational Awareness
Anomaly: Conflict NMAC; Deviation - Track / Heading All Types; Deviation / Discrepancy - Procedural Clearance
Detector: Person Air Traffic Control; Person Flight Crew
When detected: In-flight
Result: Air Traffic Control Issued Advisory / Alert; Air Traffic Control Issued New Clearance; Flight Crew Became Reoriented
Contributing factors: Weather; Aircraft; Human Factors
Primary problem: Human Factors

Narrative: I was cleared for takeoff on Runway 13L; the short runway at Boeing field; with clearance for a VFR departure from the left downwind (to the east) out to the northwest over Shilshoal. On power application; I re-checked the windsock adjacent to the north end of 13L and re-confirmed a right crosswind of between 5 to 10 KTS. My HSI was set to 310 degrees as was the heading bug. Acceleration and rotation were normal; with gear and flap retraction complete about 200 FT. At around 250 FT MSL/AGL; a startling gust of wind hit the aircraft spiking my airspeed up momentarily about 20 MPH; then diminishing. I was unaware that the gust came from either direction; and saw no clues outside that would have indicated it was now drifting me to the right. I re-stabilized my climbout; holding about 600 FPM; and maintained heading; but was completely unaware that the aircraft was now drifting to the right and into the departure centerline of Runway 13R. At about 600-650 FT MSL/AGL I heard the Tower announce 'Mooney sharp left' and interpreting that as an order for immediate turn to crosswind; banked left; at which point a small business jet passed just off to the left and over two hundred fifty feet below me; outbound (I discerned in a few minutes) from a takeoff on 13R. This was the first moment I was aware of anything wrong; or had any clue that I was off the 13L centerline; let alone in the way of 13R. Embarrassing as a concept doesn't begin to cover it.In going back over this; and even given my extensive experience and standard knowledge that you are expected - especially at BFI - to stay on centerline when launching off the small runway; some difficult complications appear affecting both this type of aircraft and this south departure off Runway 13L. First; the Mooney is a nose-high machine when cleaned up and in a climb; and it is difficult to see the horizon line over the raised nose. Up until now; unless I perceived I had a crosswind that might blow me toward the other runway in any parallel condition; I have used the standard technique of checking and rechecking my compass heading on the HSI; as I did in this case; and then secondarily looking for any visual clues off to either side that I am on track. In the case of BFI 13L; you leave the runway behind almost immediately on climb (and thus it becomes useless as an alignment cue); and you lose contact with the end of the long right runway (13R) rather soon. In this case; by the time I climbed through 300 FT and had cleaned up gear and flaps; I no longer had a clear cross-cockpit view of the right runway; and was watching; instead (and in addition to the HSI); the more distant terrain ahead and the ridgeline to my left; all of which appeared to be in the right 'place.' I was momentarily stunned to see the [business] jet pass so close and momentarily and wrongly assumed HE had somehow grossly altered course to the left to pass through the 13L extended centerline. The illogic of that resolved quickly; but that is a measure of how clueless I was (given the visual references I was watching) that I had been blown so significantly to the right.One other aspect bears mentioning: Traffic on 13L and 13R are on separate tower frequencies; which means that the tower controller has to take the time to verbally inform a short-runway departing flight that an aircraft is departing from the other; something the tower controllers do very well and continuously. When there is no time for such a call; however; or if it is not made as a courtesy; the light traffic on the left is unaware of someone larger and faster leaving from the right side (and same thing when flipped around to 31R and L). Certainly I should have been on the proper centerline regardless; but being aware of what's happening on the adjacent runway adds a margin of vigilance. I cannot honestly claim that such information in this case would have prompted me to discover my westward drift in time; but it would have helped. As a result ofthis; my primary remedy will be to pick out a more distant reference point for remaining aligned; and cheat to the east even if it means deviating left of the departure flight path (or to the right when it's to the north on 31R). I'm worried about the physiology of the aircraft in blocking forward visibility to the degree it does; but will find also some reference points on the left side (heading south from 13L); such as hangars and ramps on the south end; that I can use to check proper alignment. I will also now delay my flap retraction (in order to give me a better over the cowling climb picture) to at least the downwind. Yet another aspect is that Boeing Field's departures to the south are essentially down a valley and at lower altitudes; between rotate and approximately 800 FT; the illusion of being aligned is exacerbated because what you see to the left and right of the nose is a funnel effect that tends to visually confirm you're progressing down the 'slot' of the valley. I should also point out that in operating various aircraft in and out of BFI for many years on both runways I have never had an alignment problem before; and since this Mooney is a new aircraft for me (I have about 54 hours in her); this impresses me as a 'species-specific' aspect I should have considered before. The connection of a sudden wind shear from the left countering the expectation of the same crosswind from the right that existed on the surface; the high nose angle; the normal distractions of gear and flap retraction; and the overreliance on the proper HSI heading rather than an aggressive checking of left side clues; all connected the various links of this situation. Of course I will never let myself get into such a position again; but like all pilots who try very hard to be perfect; the fact that it occurred at all is disheartening and; at worst - if we'd had a departing jet crew not paying attention - potentially catastrophic.First; assume that the goal of remaining aligned with the appropriate runway in a parallel runway takeoff is NOT satisfied by remaining on heading or correcting for the takeoff winds. Assume only positive ground clues will suffice. Second; incorporate into specific training for such a field the need to select visual clues visible from the pilot's side that can be used to positively affirm your lateral position. To the extent that it can be done; incorporate the warning into any publication regarding local field conditions and procedures. At BFI; there has long been circulating a small and very helpful brochure which outlines the visual approach and departure procedures; and this would be an excellent place to add such a warning. Third; even though it adds to the audible workload; consider monitoring the radio channel for the OTHER runway as well as the short one (in this case monitoring 120.6 as well as 188.3) Some aircraft are not so equipped; but most will be; and this is a procedure I will weld into my pre-departure checks. Otherwise; as I say; when you operate from the short runway you are depending entirely on the controller to fill in any situational awareness needed not included in the transmissions for the frequency used on the short runway (east side; Runway 13L and 31R). And four; delay flap retraction until throttled back on downwind in order to keep a forward view of alignment clues.




Synopsis: M20 pilot reports inadvertently drifting right after takeoff from Runway 13L; into the path of a departing business jet off Runway 13R.