Posted V3452232 Sole Source SAP Justification_Redacted.pdf

V220T.12 (01/19)

Procurement Request No. V3452232

DEPARTMENT OF TRANSPORTATION

OFFICE OF THE ASSISTANT SECRETARY FOR RESEARCH AND TECHNOLOGY

VOLPE NATIONAL TRANSPORTATION SYSTEMS CENTER (VOLPE CENTER)

AVIATION WEATHER AND PNT APPLICATIONS DIVISION (V345)

SOLE SOURCE SAP JUSTIFICATION

A. Description of Supplies/Services.

The Volpe Center intends to procure one (1) Vaisala LT31 Transmissometer Part number

B2A2D1B1A1A1A1ANA1.

Background: The Federal Aviation Administration (FAA) is responsible for the acquisition, deployment and replacement of runway visual range (RVR) sensors and systems throughout the National Airspace System (NAS). These items are essential to the safe and efficient operation of airports, and especially Instrument Landing System (ILS)-equipped runways, through the determination and reporting of visibility conditions at touchdown (TD), midpoint (MP) and rollout (RO) locations of such runways. RVR information is used to inform pilots on prevailing visibility conditions for guidance during the execution of takeoffs and landings, and thus impacting the safety and efficiency of airport operations. Tasker 500 transmissometers were deployed by the FAA for RVR use beginning in the 1960s to replace measurements made by human observers. They have since been replaced by forward scatter meter-based instruments for wide operational use because they require less maintenance, calibration, and space than the originally deployed transmissometer systems. However, because transmissometer technology more closely duplicates human vision, because of the ability to calibrate transmissometers without reference to other instruments, and because of the long operational validation of transmissometer measurements, transmissometer measurements are still used as the gold standard to verify and validate these new instruments.

On behalf of the FAA, Volpe operates the Aviation Weather Research Facility (AWRF) located at Joint Base Cape Cod. Volpe has previously identified the Vaisala LT31 transmissometer as a replacement for the Tasker 500 transmissometer, and tested the Vaisala LT31 transmissometer during the “Change of the Tasker 500 Transmissometer Gold Standard”. This project took place in two phases. During Phase I of the effort, a market survey of transmissometer options, informed by a literature review and independent research, identified the Vaisala LT31 as the most suitable replacement for the existing standard transmissometer (the Tasker 500).

Volpe made the recommendation to the FAA that the LT31 be selected for testing, and designed a test plan for the validation effort, purchased an LT31, and installed it for validation. During Phase II of the effort, Volpe conducted a 12-month field test and side-by-side validation of the LT31 with the Tasker 500, which identified the performance of the LT31 as adequate to serve as the new reference transmissometer. A reproduction of the market research performed during the prior acquisition, along with the supporting rationale, is included in in an Appendix with sections B (Market Research) and C (Supporting Rationale) from the prior acquisition below.

During the evaluation of the LT31, the FAA was informed by the manufacturer of the existing PC-RVR forward scatter meters used widely throughout the country that the PC-RVR sensors will stop being manufactured and supported within a few years. As a result, the FAA engaged Volpe to test a proposed replacement sensor, which is an adapted version of the Vaisala FD70.

In order to perform the testing of the FD70 for the FAA, the Volpe Center needs to acquire a second transmissometer. Two transmissometers arranged in a cross pattern is required to accurately assess atmospheric homogeneity, which is an element of the FAA’s forward scatter meter performance standard. The LT31 is the only transmissometer which has undergone a 12-month data collection period, followed by analysis, indicating that its performance is adequate to serve as a replacement for the Tasker 500 sensors. Acquiring this second

D. Required Signatures. The following signatures represent concurrence/approval of this justification:

Christopher Scarpone Stephen Mackey PR Technical Initiator Date PR Technical Initiator’s Supervisor Date

Contracting Officer Date Chief, Contracts Branch (or designee) Date (Signature required for procurements over $25,000)

CHRISTOPHER

WILLIAM DOOLEY

Digitally signed by CHRISTOPHER

WILLIAM DOOLEY

Date: 2023.06 27 14:31:09 -04'00'

CHRISTOPHER

WILLIAM DOOLEY

Digitally signed by CHRISTOPHER

WILLIAM DOOLEY

Date: 2023.06.27 14:31:41 -04'00'

Currently Manufactured / Commercially Available:

Because the entire purpose of this project is to remove the existing inability to source replacement components for the Tasker 500, which is the current gold standard transmissometer, a replacement must be currently manufactured and commercially available. An instrument that is out of production or is not made available commercially will either have limited-to-no support available, or be simply not for sale. The Vaisala LT31 is the only commercially available, currently manufactured transmissometer that meets all of the Government’s performance requirements as detailed below.

Accommodates 250’ Baseline:

In order to validate the performance of any new instrument, it must be compared against a standard.

Transmissometers consist of a projector-receiver pair; the projector emits light, and the receiver senses the light reaching it, which has not been absorbed or scattered by the intervening atmosphere. The distance between the projector and receiver is known as the “baseline”, and the baseline distance is a key parameter for transmissometer operation. It determines the measurement range of the instrument and the physical region of atmosphere that is sampled to provide the visibility measurement.

In order for a valid comparison to be made between two transmissometer systems, the systems must be as close as practicable, and with the same baseline, to ensure the atmosphere the systems measure is as similar as possible. The existing Tasker 500 system used as the gold standard has a 250-foot baseline distance, which has been operationally validated through use in the NAS and allows the transmissometer to measure operationally relevant RVR distances. A change of baseline would require extensive testing to validate results of the new baseline against the existing baseline, which is timeline- and cost-prohibitive. Therefore, any proposed gold standard transmissometer should be able to conform to the existing 250 foot baseline of the Tasker 500. The Vaisala LT31 datasheet indicates that it supports 75 meters (~250 feet) as a recommended baseline length.

Meets ICAO Annex 3 Performance Standards:

After ensuring the two transmissometers are measuring similar volumes of air, the new system must be evaluated for accuracy. It must agree well enough with the existing standard to be confident in using it as a replacement. In conjunction with the FAA, Volpe has determined that the appropriate accuracy requirement is the FAA requirement that is already used for validation of new RVR systems, FAA E 2772B (“PERFORMANCE SPECIFICATION PC BASED RUNWAY VISUAL RANGE (RVR) SYSTEM”). This specification requires, in section 3.2.2.3.5(a), that:

Under homogeneous atmospheric conditions, [new RVR system] measurements shall agree with those of a reference transmissometer to within 15 % (standard deviation) for (reference) 3 km-1 [RVR < 1000 m (3281 ft)]. The 15 %-standard-deviation requirement is tested at the 90 % confidence level; that is, 90 % of the one-minute-average readings of the scatter meter shall agree to within ±25 % with the simultaneous one-minute-average readings of the reference transmissometer(s). Outliers (that is, more than a factor two difference) shall not occur for more than 0.2 % of the measurements.

Because the FAA has not had a requirement for transmissometers in many years, no manufacturer advertises that their instrument can meet this specification. However, transmissometer systems are in wider use globally, and the ICAO sets similar accuracy recommendations in Meteorological Services for International Air Navigation (Annex 3 to the Convention on International Civil Aviation). Attachment A specifies that the “Operationally Desirable Accuracy” for RVR measurement is:

- ± 10 m (33 ft) up to 400 m (1312 ft)

- ± 25 m (82 ft) between 400 m and 800 m (1312 ft to 2625 ft)

- ± 10% above 800 m (4921 ft)

While the two specifications are not identical, for a 250 foot baseline transmissometer (which is capable of accurately measuring RVR from 37.5 m – 1500+ m (123 – 4921+ ft), an instrument that meets ICAO guidelines will have the following accuracy, expressed as a percentage to correspond to the FAA specification:

- 27% error for 37.5 m reducing to 2.5% error at 400 m

- 6.25% error for 401 m reducing to 3.1% error at 800 m

- 10% error above 800 m

Any instrument meeting the ICAO Annex 3 standards would meet the FAA specification. For that reason, procurement of an instrument claiming Annex 3 compliance is much less likely to waste funding on an instrument that ultimately turns out to have inadequate performance. According to the Vaisala LT31 datasheet, the LT31 “exceeds the ICAO (Annex 3) recommendations.”

Automatic Self-Calibration / Alignment / Window Compensation:

Because of their basis of operation, transmissometers are especially vulnerable to issues with calibration, alignment, and window contamination. The receiver must be extremely sensitive to incident light in order to accurately measure visibility. For example, in order to meet ICAO Annex 3 requirements, the transmissometer must be able to distinguish between 23.4% of the projected light reaching the receiver (400 m visibility with a 75 m baseline) and 22.9% of the projected light reaching the receiver (390 m visibility with a 75 m baseline). Any slight changes in alignment (for example, as the result of frost heave) or window contamination (from dirt or weather contaminants) affect the ability of the receiver to accurately measure the amount of light attenuated by the atmosphere. Because of the remote nature of the AWRF, a new gold standard instrument should be able to compensate for these factors to maintain accurate measurement. The Vaisala LT31 includes automatic self-calibration, automatic fine alignment, and automatic window contamination compensation mechanisms. It monitors atmospheric conditions automatically to identify appropriate conditions for calibration and automatically self-calibrates when those conditions are met. It performs automatic alignment optimization and adjustment via servomechanisms. It directly measures window transmissivity to perform automatic window contamination compensation.

The market research effort described above concluded that the transmissometer market is not very broad, presumably because of the transition of aviation service providers like the FAA to forward scatter meters for operational use.

Based on the market research, and as summarized in Table 1, the Vaisala LT31 is the only commercially available product that meets the Volpe Center’s requirement.

Development of a new transmissometer that meets the government’s performance requirements is not feasible.

Transmissometers are precision optical instruments requiring sophisticated design, manufacturing, and quality control practices. A clean-sheet design of a new instrument would take several years and at least hundreds of thousands, if not millions of dollars. Acquisition and testing of a new instrument in the near future is key to allow validation to proceed while it is still possible to maintain and operate the existing gold standard instrument.